diff --git "a/notes/gray-anatomy_8.txt" "b/notes/gray-anatomy_8.txt" new file mode 100644--- /dev/null +++ "b/notes/gray-anatomy_8.txt" @@ -0,0 +1,9040 @@ + + +Dorsum sellae + +Foramen lacerum +Foramen ovale +Trigeminal impression + +Groove and hiatus +for greater petrosal nerve + +Arcuate eminence + +Opening of carotid canal +Groove for middle meningeal artery + + + + +Foramen spinosum + + + +Fig. 8.26 Middle cranial fossa. 855 +Head and Neck + + + +oculomotor nerve [III], the trochlear nerve [IV], the oph-thalmic nerve [V1], the abducent nerve [VI], and ophthal-mic veins. +Posterior to the medial end of the superior orbital fissure on the floor of the middle cranial fossa is a rounded foramen projecting in an anterior direction (the foramen rotun-dum), through which the maxillary nerve [V2] passes from the middle cranial fossa to the pterygopalatine fossa. +Posterolateral to the foramen rotundum is a large oval opening (the foramen ovale), which allows struc-tures to pass between the extracranial infratemporal fossa and the middle cranial fossa. The mandibular nerve [V3], lesser petrosal nerve (carrying fibers from the tympanic plexus that originally came from the glossopharyngeal nerve [IX]) and, occasionally, a small vessel (the accessory middle meningeal artery), pass through this foramen. +Posterolateral from the foramen ovale is the small foramen spinosum (Fig. 8.26). This opening also connects the infratemporal fossa with the middle cranial fossa. The middle meningeal artery and its associated veins pass through this foramen and, once inside, the groove for the middle meningeal artery across the floor and lateral wall of the middle cranial fossa clearly marks their path. +Posteromedial to the foramen ovale is the rounded intracranial opening of the carotid canal. Directly inferior to this opening is an irregular foramen (the foramen lacerum) (Fig. 8.26). Clearly observed in the inferior view of the skull, the foramen lacerum is closed in life by a cartilaginous plug, and no structures pass through it completely. + +Temporal bone +The posterior boundary of the middle cranial fossa is formed by the anterior surface of the petrous part of the petromastoid part of the temporal bone. +Medially, there is a slight depression (trigeminal impression) in the anterior surface of the petrous part of the temporal bone (Fig. 8.26), which marks the location of the sensory ganglion for the trigeminal nerve [V]. +Lateral to the trigeminal impression and on the anterior surface of the petrous part of the temporal bone is a small linear groove that passes in a superolateral direction and ends in a foramen (the groove and hiatus for the greater petrosal nerve). The greater petrosal nerve is a branch of the facial nerve [VII]. +Anterolateral to the groove for the greater petrosal nerve is a second, smaller groove and hiatus for the lesser petrosal nerve, a branch from the tympanic plexus carrying fibers that originally came from the glossopha-ryngeal nerve [IX] (Fig. 8.26). +Above and lateral to the small openings for the greater 856 and lesser petrosal nerves, near the superior ridge of the + +petrous part of the temporal bone, is a rounded protrusion of bone (the arcuate eminence) produced by the underly-ing anterior semicircular canal of the inner ear. +Just anterior and lateral to the arcuate eminence the anterior surface of the petrous part of the temporal bone is slightly depressed. This region is the tegmen tympani, and marks the thin bony roof of the middle ear cavity. + +Posterior cranial fossa +The posterior cranial fossa consists mostly of parts of the temporal and occipital bones, with small contributions from the sphenoid and parietal bones (Fig. 8.27). It is the largest and deepest of the three cranial fossae and contains the brainstem (midbrain, pons, and medulla) and the cerebellum. + +Boundaries +The anterior boundaries of the posterior cranial fossa in the midline are the dorsum sellae and the clivus (Fig. 8.27). The clivus is a slope of bone that extends upward from the foramen magnum. It is formed by contributions from the body of the sphenoid and from the basilar part of the occipital bone. +Laterally the anterior boundaries of the posterior cranial fossa are the superior border of the petrous part of the petromastoid part of the temporal bone. +Posteriorly the squamous part of the occipital bone to the level of the transverse groove is the major boundary, while laterally the petromastoid part of the temporal bone and small parts of the occipital and parietal bones border the fossa. + +Foramen magnum +Centrally, in the deepest part of the posterior cranial fossa, is the largest foramen in the skull, the foramen magnum. It is surrounded by the basilar part of the occipi-tal bone anteriorly, the lateral parts of the occipital bone on either side, and the squamous part of the occipital bone posteriorly. +The spinal cord passes superiorly through the foramen magnum to continue as the brainstem. +Also passing through the foramen magnum are the vertebral arteries, the meninges, and the spinal roots of the accessory nerve [XI]. + +Grooves and foramina +The clivus slopes upward from the foramen magnum. Lateral to the clivus is a groove for the inferior petrosal sinus between the basilar part of the occipital bone and the petrous part of the petromastoid part of the temporal bone (Fig. 8.27). +Regional Anatomy • Cranial Cavity 8 + + + + + + +Groove for inferior petrosal sinus +Superior border of petrous part of temporal bone + +Groove for sigmoid sinus + + + + + + + + + +Groove for transverse sinus + + +Internal occipital crest + +Clivus +Jugular tubercle + +Internal acoustic meatus + +Jugular foramen + +Hypoglossal canal + + + + + + + + + + +Foramen magnum + + +Internal occipital protuberance + + +Fig. 8.27 Posterior cranial fossa. + + + + + +Laterally, across the upper half of the posterior surface of the petrous part of the temporal bone, is an oval foramen (the internal acoustic meatus). The facial [VII] and vestibulocochlear [VIII] nerves, and the labyrinthine artery + + +Squamous part of the occipital bone +The squamous part of the occipital bone has several promi-nent features (Fig. 8.27): + + + +pass through it. +Inferior to the internal acoustic meatus the temporal bone is separated from the occipital bone by the large jugular foramen (Fig. 8.27). Leading to this foramen from the medial side is the groove for the inferior petrosal sinus, and from the lateral side the groove for the sigmoid sinus. +The sigmoid sinus passes into the jugular foramen, and is continuous with the internal jugular vein, while the inferior petrosal sinus empties into the internal jugular vein in the area of the jugular foramen. +Also passing through the jugular foramen are the glos-sopharyngeal nerve [IX], the vagus nerve [X], and the accessory nerve [XI]. +Medial to the jugular foramen is a large rounded mound + + +■ Running upward in the midline from the foramen magnum is the internal occipital crest. +■ On either side of the internal occipital crest, the floor of the posterior cranial fossa is concave to accommo-date the cerebellar hemispheres. +■ The internal occipital crest ends superiorly in a bony prominence (the internal occipital protuberance). +■ Extending laterally from the internal occipital protuber-ance are grooves produced by the transverse sinuses, which continue laterally, eventually joining a groove for each sigmoid sinus—each of these grooves then turns inferiorly toward the jugular foramina. + +The transverse and sigmoid sinuses are intradural + + + +of the occipital bone (the jugular tubercle). Just inferior to this, and superior to the foramen magnum, is the hypo-glossal canal, through which the hypoglossal nerve [XII] leaves the posterior cranial fossa, and a meningeal branch of the ascending pharyngeal artery enters the posterior cranial fossa. +Just posterolateral to the hypoglossal canal is the small condylar canal that, when present, transmits an emis-sary vein. + +venous sinuses. + +Foramina and fissures through which major structures enter and leave the cranial cavity +Foramina and fissures through which major structures pass between the cranial cavity and other regions are sum-marized in Fig. 8.28. + +857 +Head and Neck + + + +Foramen rotundum: (middle cranial fossa/ pterygopalatine fossa) • [V2] Maxillary division +of [V] (trigeminal nerve) +Foramen ovale: (middle cranial fossa/ infratemporal fossa) +• [V3] Mandibular division of [V] (trigeminal nerve) +Carotid canal: +(middle cranial fossa/neck) • Internal carotid artery + +Foramen spinosum: (middle cranial fossa/ infratemporal fossa) +• Middle meningeal artery +Jugular foramen: +(posterior cranial fossa/neck) • [IX] Glossopharyngeal nerve • [X] Vagus nerve +• [XI] Accessory nerve • Internal jugular vein + + +Foramen magnum: (posterior cranial fossa/neck) • Spinal cord +• Vertebral arteries +Roots of accessory nerve [XI] pass from +upper region of spinal cord through the foramen magnum into the cranial cavity and then leave +the cranial cavity through the jugular foramen + +A + + +Carotid canal: +• Internal carotid artery + + + + + +Stylomastoid foramen: • [VII] Facial nerve + + +Cribriform plate: +(anterior cranial fossa/nasal cavity) • [I] Olfactory nerves + +Optic canal: +(middle cranial fossa/orbit) • [II] Optic nerve +• Ophthalmic artery + +Superior orbital fissure: (middle cranial fossa/orbit) • [V1] Ophthalmic division +of [V] (trigeminal nerve) • [III] Oculomotor nerve +• [IV] Trochlear nerve • [VI] Abducent nerve +• Superior ophthalmic vein + +Foramen lacerum +(filled with cartilage in life) + + +Internal acoustic meatus: (posterior cranial fossa/ear, and neck via stylomastoid foramen) +• [VII] Facial nerve +• [VIII] Vestibulocochlear nerve +Labyrnthine artery and vein + +Hypoglossal canal: (posterior cranial fossa/neck) • [XII] Hypoglossal nerve + + +Foramen ovale: +• [V3] Mandibular division of [V] (trigeminal nerve) + +Foramen spinosum: +• Middle meningeal artery + + + +Hypoglossal canal: +• [XII] Hypoglossal nerve + + +Jugular foramen: +• [IX] Glossopharyngeal nerve • [X] Vagus nerve +• [XI] Accessory nerve • Internal jugular vein + + +Foramen magnum: • Spinal cord +• Vertebral arteries +Roots of accessory nerve [XI] pass from +upper region of spinal cord through the foramen magnum into the cranial cavity and then leave the cranial cavity through the jugular foramen +B + + + +858 + +Fig. 8.28 Summary of foramina and fissures through which major structures enter and leave the cranial cavity. A. Floor of cranial cavity. Also indicated are the regions between which each foramen or fissure communicates. B. Inferior aspect of cranium. +Regional Anatomy • Cranial Cavity 8 + + +In the clinic + +Craniosynostosis +Some babies can be born with ossified fusion (synostosis) of one or more of the cranial sutures. This can result in an irregular head shape because the pattern and direction of skull growth are altered. In the majority of cases the cause is unknown, and in a minority of cases it may be caused by a genetic syndrome. + + + + + + + + +In the clinic + +Medical imaging of the head Radiography +Until recently, the standard method of imaging the head was plain radiography. The radiographs are taken in three standard projections—the posteroanterior view, the lateral view, and the Towne’s view (anteroposterior [AP] axial— head in anatomical position). Additional views are obtained to assess the foramina at the base of the skull and the facial bones. Currently, skull radiographs are used in cases of trauma, but such use is declining. Skull fractures are relatively easily detected (Fig. 8.29). The patient is assessed and treatment is based upon the underlying neurological or potential neurological complications. +Computed tomography +Since the development of computed tomography (CT), cerebral CT has become the “workhorse” of neuroradiological examination. It is ideally used for head injury because the brain and its coverings can be easily and quickly examined and blood is easily detected. By altering the mathematical algorithm of the data set the bones can also be demonstrated. +With intravenous contrast, CT angiography can be used to demonstrate the position and the size of an intracerebral aneurysm before endovascular treatment. +Magnetic resonance imaging +Magnetic resonance imaging (MRI) is unsurpassed by other imaging techniques in its ability for contrast resolution. The brain and its coverings, cerebrospinal fluid (CSF), and vertebral column can be easily and quickly examined. Newer imaging sequences permit CSF suppression to define periventricular lesions. +Magnetic resonance angiography has been extremely useful in determining the completeness of the intracranial vasculature (circle of Willis), which is necessary in some surgical conditions. +MRI is also a powerful tool in the assessment of carotid stenosis. + + + +Ultrasonography +It is now possible to carry out intracranial Doppler studies, which enable a surgeon to detect whether a patient is experiencing cerebral embolization from a carotid plaque. +Extracranial ultrasound is extremely important in tumor staging and in assessing neck masses and the carotid bifurcation (Fig. 8.30). +Ultrasound is useful in children because they have an acoustic window through the fontanelles. + + + +Skull fracture + + + + + + + + + + + + + + + + + + + + + +Fig. 8.29 Skull fracture seen on a skull radiograph (patient in supine position). + +(continues) + +859 +Head and Neck + + +In the clinic—cont’d + +External carotid artery Common carotid artery Common carotid artery + + + + + + + + + + + + + + +B + +Internal carotid artery stenosis + + +A + +Internal carotid artery + +Fig. 8.30 Ultrasound scans. A. Normal carotid bifurcation. B. Internal carotid artery stenosis. + + + + + +In the clinic + +Fractures of the skull vault +The skull vault is a remarkably strong structure because it protects our most vital organ, the brain. The shape of the skull vault is of critical importance and its biomechanics prevent fracture. From a clinical standpoint skull fractures alert clinicians to the nature and force of an injury and potential complications. The fracture itself is usually of little consequence (unlike, say, a fracture of the tibia). Of key importance is the need to minimize the extent of primary brain injury and to treat potential secondary complications, rather than focusing on the skull fracture. Skull fractures that have particular significance include depressed skull fractures, compound fractures, and pterion fractures. +Depressed skull fractures +In a depressed skull fracture a bony fragment is depressed below the normal skull convexity. This may lead to secondary arterial and venous damage with hematoma formation. A primary brain injury can also result from this type of fracture. +Compound fractures +In a compound fracture there is a fracture of the bone 860 together with a breach of the skin, which may allow an + + + +infection to enter. Typically these fractures are associated with scalp lacerations and can usually be treated with antibiotics. +Important complications of compound fractures include meningitis, which may be fatal. +A more subtle type of compound fracture involves fractures across the sinuses. These may not be appreciated on first inspection, but are an important potential cause of morbidity and should be considered in patients who develop intracranial infections secondary to trauma. +Pterion fractures +The pterion is an important clinical point on the lateral aspect of the skull. At the pterion the frontal, parietal, greater wing of the sphenoid, and temporal bones come together. Importantly, deep to this structure is the middle meningeal artery. An injury to this point of the skull is extremely serious because damage to this vessel may produce a significant extradural hematoma, which can be fatal. +Regional Anatomy • Meninges 8 + + + +MENINGES + +The brain, as well as the spinal cord, is surrounded by three + +■ The outer periosteal layer is firmly attached to the skull, is the periosteum of the cranial cavity, contains the meningeal arteries, and is continuous with the + +layers of membranes (the meninges, Fig. 8.31A)—a periosteum on the outer surface of the skull at the + +tough, outer layer (the dura mater), a delicate, middle layer (the arachnoid mater), and an inner layer firmly attached to the surface of the brain (the pia mater). +The cranial meninges are continuous with, and similar to, the spinal meninges through the foramen magnum, with one important distinction—the cranial dura mater consists of two layers, and only one of these is continuous + +foramen magnum and other intracranial foramina (Fig. 8.31B). +■ The inner meningeal layer is in close contact with the arachnoid mater and is continuous with the spinal dura mater through the foramen magnum. + +The two layers of dura separate from each other at + + + +through the foramen magnum (Fig. 8.31B). + +Cranial dura mater + +numerous locations to form two unique types of structures (Fig. 8.31A): + + + +The cranial dura mater is a thick, tough, outer covering of the brain. It consists of an outer periosteal layer and an inner meningeal layer (Fig. 8.31A): + +■ dural partitions, which project inward and incompletely separate parts of the brain, and +■ intracranial venous structures. + + + + + +Pia mater +Arachnoid mater + + +Intracranial venous structure +Skull (superior sagittal sinus) Inner meningeal layer of dura mater + +Dura mater Outer periosteal layer of dura mater + +Subarachnoid space + + + + + + + + + + + + + +A + +Dural partition (falx cerebri) + +Meningeal layer of dura mater Foramen magnum Skull + +Periosteal layer of dura mater + + + + +Periosteum + +Spinal dura mater + +Spinal extradural space +Vertebra CI + + + +B + +Fig. 8.31 Cranial meninges. A. Superior coronal view. B. Continuity with the spinal meninges. 861 +Head and Neck + + + + +Dural partitions +The dural partitions project into the cranial cavity and partially subdivide the cranial cavity. They include the falx cerebri, tentorium cerebelli, falx cerebelli, and dia-phragma sellae. + +Falx cerebri +The falx cerebri (Fig. 8.32) is a crescent-shaped down-ward projection of meningeal dura mater from the dura lining the calva that passes between the two cerebral hemispheres. It is attached anteriorly to the crista galli of the ethmoid bone and frontal crest of the frontal bone. Posteriorly it is attached to and blends with the tentorium cerebelli. + +Tentorium cerebelli +The tentorium cerebelli (Fig. 8.32) is a horizontal projec-tion of the meningeal dura mater that covers and sepa-rates the cerebellum in the posterior cranial fossa from the posterior parts of the cerebral hemispheres. It is attached posteriorly to the occipital bone along the grooves for the transverse sinuses. Laterally, it is attached to the + +superior border of the petrous part of the temporal bone, ending anteriorly at the anterior and posterior clinoid processes. +The anterior and medial borders of the tentorium cer-ebelli are free, forming an oval opening in the midline (the tentorial notch), through which the midbrain passes. + +Falx cerebelli +The falx cerebelli (Fig. 8.32) is a small midline projection of meningeal dura mater in the posterior cranial fossa. It is attached posteriorly to the internal occipital crest of the occipital bone and superiorly to the tentorium cerebelli. Its anterior edge is free and is between the two cerebellar hemispheres. + +Diaphragma sellae +The final dural projection is the diaphragma sellae (Fig. 8.32). This small horizontal shelf of meningeal dura mater covers the hypophyseal fossa in the sella turcica of the sphenoid bone. There is an opening in the center of the diaphragma sellae through which passes the infundibu-lum, connecting the pituitary gland with the base of the brain, and any accompanying blood vessels. + + + + + + + +Tentorium cerebelli +Falx cerebri + +Tentorial notch Infundibulum + + + +Borders of +tentorial notch Falx cerebri + + + + + + + +Falx cerebelli + + + + +Tentorium cerebelli + + +Tentorium cerebelli +A Diaphragma sellae B Diaphragma sellae + +Fig. 8.32 Dural partitions. A. Diagram. B. Dissection. + + +862 +Regional Anatomy • Meninges 8 + + +Arterial supply +The arterial supply to the dura mater (Fig. 8.33) travels in the outer periosteal layer of the dura and consists of: + + +■ The posterior branch passes in a posterosuperior direc-tion, supplying this region of the middle cranial fossa. + + + + +■ anterior meningeal arteries in the anterior cranial fossa, +■ the middle and accessory meningeal arteries in the middle cranial fossa, and +■ the posterior meningeal artery and other meningeal branches in the posterior cranial fossa. + +The accessory meningeal artery is usually a small branch of the maxillary artery that enters the middle cranial fossa through the foramen ovale and supplies areas medial to this foramen. +The posterior meningeal artery and other meningeal branches supplying the dura mater in the posterior cranial fossa come from several sources (Fig. 8.33): + + + +All are small arteries except for the middle meningeal artery, which is much larger and supplies the greatest part of the dura. +The anterior meningeal arteries are branches of the ethmoidal arteries. +The middle meningeal artery is a branch of the maxil-lary artery. It enters the middle cranial fossa through the foramen spinosum and divides into anterior and posterior branches: + +■ The posterior meningeal artery, the terminal branch of the ascending pharyngeal artery, enters the poste-rior cranial fossa through the jugular foramen. +■ A meningeal branch from the ascending pharyngeal artery enters the posterior cranial fossa through the hypoglossal canal. +■ Meningeal branches from the occipital artery enter the posterior cranial fossa through the jugular foramen and the mastoid foramen. +■ A meningeal branch from the vertebral artery arises + + + +■ The anterior branch passes in an almost vertical direc-tion to reach the vertex of the skull, crossing the pterion during its course. + +as the vertebral artery enters the posterior cranial fossa through the foramen magnum. + + + +Posterior meningeal artery (from ascending pharyngeal artery) + + + +Position of pterion Meningeal branch (from ascending pharyngeal artery) + + +Middle meningeal artery + + +Anterior meningeal arteries (from ethmoidal arteries) + + +Middle meningeal artery + + + +Maxillary artery + + + + + + + +Fig. 8.33 Dural arterial supply. + + +Meningeal branch (from occipital artery) + +Meningeal branch (from vertebral artery) +Ascending pharyngeal artery + +Occipital artery +External carotid artery + + + +863 +Head and Neck + + + +Innervation +Innervation of the dura mater (Fig. 8.34) is by small men-ingeal branches of all three divisions of the trigeminal nerve [V1, V2, and V3], the vagus nerve [X], and the first, second, and, sometimes, third cervical nerves. (Possible involvement of the glossopharyngeal [IX] and hypoglossal nerves [XII] in the posterior cranial fossa has also been + + +mater (Fig. 8.35). From its inner surface thin processes or trabeculae extend downward, cross the subarachnoid space, and become continuous with the pia mater. +Unlike the pia, the arachnoid does not enter the grooves or fissures of the brain, except for the longitudinal fissure between the two cerebral hemispheres. + +reported.) +In the anterior cranial fossa meningeal branches from the ethmoidal nerves, which are branches of the ophthal-mic nerve [V1], supply the floor and the anterior part of the falx cerebri. +Additionally, a meningeal branch of the ophthalmic nerve [V1] turns and runs posteriorly, supplying the tento-rium cerebelli and the posterior part of the falx cerebri. +The middle cranial fossa is supplied medially by menin-geal branches from the maxillary nerve [V2] and laterally, along the distribution of the middle meningeal artery, by meningeal branches from the mandibular nerve [V3]. +The posterior cranial fossa is supplied by meningeal branches from the first, second, and, sometimes, third cervical nerves, which enter the fossa through the foramen magnum, the hypoglossal canal, and the jugular foramen. Meningeal branches of the vagus nerve [X] have also been described. (Possible contributions from the glossopharyn-geal [IX] and hypoglossal [XII] nerves have also been reported.) + +Arachnoid mater +The arachnoid mater is a thin, avascular membrane that lines, but is not adherent to, the inner surface of the dura + + +Arachnoid granulations + +Cerebral artery + + +Cervical nerves + + + + + + + + + + + + + + + + +Ophthalmic division of +trigeminal nerve [V1] (tentorium cerebelli) +Mandibular division of trigeminal nerve [V3] +Maxillary division of trigeminal nerve [V2] + +Fig. 8.34 Dural innervation. + + + +Superior sagittal sinus + +Cerebral vein + + +Ophthalmic division of +trigeminal nerve [V1] (falx cerebri) + + + + + + + + + + + + + + + + + + +Ophthalmic division of trigeminal nerve [V1] + + + + +Dura mater + +External table +Diploë Skull +Internal table + + + +Arachnoid mater + +Pia mater + + +Extradural space (potential space) + +Subarachnoid space + + + + + + + + + + +864 Fig. 8.35 Arrangement of the meninges and spaces. +Regional Anatomy • Meninges 8 + + + + +Pia mater +The pia mater is a thin, delicate membrane that closely invests the surface of the brain (Fig. 8.35). It follows the contours of the brain, entering the grooves and fissures on its surface, and is closely applied to the roots of the cranial nerves at their origins. + + +Arrangement of meninges and spaces +There is a unique arrangement of meninges coupled with real and potential spaces within the cranial cavity (Fig. 8.35). A potential space is related to the dura mater, while a real space exists between the arachnoid mater and the pia +mater. + +Extradural space +The potential space between dura mater and bone is the extradural space (Fig. 8.35). Normally, the outer or periosteal layer of dura mater is firmly attached to the bones surrounding the cranial cavity. +This potential space between dura and bone can become a fluid-filled actual space when a traumatic event results in a vascular hemorrhage. Bleeding into the extradural space primarily due to rupture of a meningeal artery or less often from a torn dural venous sinus results in an extradural hematoma. + +Subdural space +Anatomically, a true subdural space does not exist. Blood collecting in this region (subdural hematoma) due to injury represents a dissection of the dural border cell layer, which + + + +In the clinic + +Hydrocephalus +Hydrocephalus is a dilation of the cerebral ventricular system, which is due to either an obstruction to the flow of CSF, an overproduction of CSF, or a failure of reabsorption of CSF. +Cerebrospinal fluid is secreted by the choroid plexus within the lateral, third, and fourth ventricles of the brain. As it is produced it passes from the lateral ventricles through the interventricular foramina (the foramina of Monro) to enter the third ventricle. From the third ventricle it passes through the cerebral aqueduct (aqueduct of Sylvius) into the fourth ventricle, and from here it passes into the subarachnoid space via the midline foramen or the two lateral foramina (foramen of Magendie and foramina of Luschka). + +is the innermost lining of the meningeal dura. Dural border cells are flattened cells surrounded by extracellular spaces filled with amorphous material. While very infrequent, an occasional cell junction may be seen between these cells and the underlying arachnoid layer. Bleeding due to the tearing of a cerebral vein as it crosses through the dura to enter a dural venous sinus can result in a subdural hematoma. + +Subarachnoid space +Deep to the arachnoid mater is the only normally occur-ring fluid-filled space associated with the meninges, the subarachnoid space (Fig. 8.35). It occurs because the arachnoid mater clings to the inner surface of the dura mater and does not follow the contour of the brain, while the pia mater, being against the surface of the brain, closely follows the grooves and fissures on the surface of the brain. The narrow subarachnoid space is therefore created between these two membranes (Fig. 8.35). +The subarachnoid space surrounds the brain and spinal cord and in certain locations it enlarges into expanded areas (subarachnoid cisterns). It contains cerebrospinal fluid (CSF) and blood vessels. +Cerebrospinal fluid is produced by the choroid plexus, primarily in the ventricles of the brain. It is a clear, color-less, cell-free fluid that circulates through the subarachnoid space surrounding the brain and spinal cord. +The CSF returns to the venous system through arach-noid villi. These project as clumps (arachnoid granula-tions) into the superior sagittal sinus, which is a dural venous sinus, and its lateral extensions, the lateral lacunae (Fig. 8.35). + + + + + +The CSF passes around the spinal cord inferiorly, envelops the brain superiorly, and is absorbed through the arachnoid granulations in the walls of the dural venous sinuses. In adults almost half a liter of CSF is produced +per day. +In adults the commonest cause of hydrocephalus is an interruption of the normal CSF absorption through the arachnoid granulations. This occurs when blood enters the subarachnoid space after subarachnoid hemorrhage, passes over the brain, and interferes with normal CSF absorption. To prevent severe hydrocephalus it may be necessary to place a small catheter through the brain into the ventricular system to relieve the pressure. +Other causes of hydrocephalus include congenital obstruction of the aqueduct of Sylvius and a variety of +(continues) 865 +Head and Neck + + + +In the clinic—cont’d + +tumors (e.g., a midbrain tumor), where the mass obstructs the aqueduct. Rare causes include choroid plexus tumors that secrete CSF. +In children, hydrocephalus is always dramatic in its later stages. The hydrocephalus increases the size and dimensions of the ventricle, and as a result the brain enlarges. Because the skull sutures are not fused, the head expands. Cranial enlargement in utero may make a vaginal delivery + + +In the clinic + +Cerebrospinal fluid leak +Leakage of CSF from the subarachnoid space may occur after any procedure in and around the brain, spinal cord, and meningeal membranes. These procedures include lumbar spine surgery, epidural injection, and CSF aspiration. + + +In the clinic + +Meningitis +Meningitis is a rare infection of the leptomeninges (the leptomeninges are a combination of the arachnoid mater and the pia mater). Infection of the meninges typically occurs via a blood-borne route, though in some cases it may be by direct spread (e.g., trauma) or from the nasal cavities through the cribriform plate in the ethmoid bone. +Certain types of bacterial inflammation of the meninges are so virulent that overwhelming inflammation and sepsis with cerebral irritation can cause the patient to rapidly pass into a coma and die. +Meningitis is usually treatable with antibiotics. + + + +impossible, and delivery then has to be by caesarean section. +Both CT and MRI enable a radiologist to determine the site of obstruction and in most cases the cause of the obstruction. A distinction must be made between ventricular enlargement due to hydrocephalus and that due to a variety of other causes (e.g., cerebral atrophy). + + + + + +In “cerebrospinal fluid leak” syndrome, CSF leaks out of the subarachnoid space and through the dura mater for no apparent reason. The clinical consequences of this include dizziness, nausea, fatigue, and a metallic taste in the mouth. Other effects also include facial nerve weakness and double vision. + + + + +Certain types of bacteria that produce meningitis produce other effects; for example, subcutaneous hemorrhage (ecchymoses) is a feature of meningococcal meningitis. +The typical history of meningitis is nonspecific at first. The patient may have mild headache, fever, drowsiness, and nausea. As the infection progresses, photophobia (light intolerance) and ecchymosis may ensue. Straight leg raising causes marked neck pain and discomfort (Kernig’s sign) and an emergency hospital admission is warranted. +Immediate treatment consists of very-high-dose intravenous antibiotics and supportive management. + + + + + +In the clinic + +Brain tumors +Determination of the anatomical structure from which a tumor arises is of the utmost importance, particularly when it arises within the cranial vault. Misinterpretation of the location of a lesion and its site of origin may have devastating consequences for the patient. +When assessing any lesion in the brain, it is important to define whether it is intra-axial (within the brain) or +extra-axial (outside the brain). +Typical extra-axial tumors include meningiomas (tumors of the meninges) and acoustic neuromas. Meningiomas typically arise from the meninges, with preferred sites including regions at and around the falx cerebri, the free edge of the tentorium cerebelli, and the anterior margin of +866 the middle cranial fossa. Acoustic neuromas are typically at + + + +and around the vestibulocochlear nerve [VIII] and in the cerebellopontine angle. +Intra-axial lesions are either primary or secondary. By far the commonest type are the secondary brain lesions, which in most cases are metastatic tumor deposits. +Metastatic tumor lesions are typically found in patients with either breast carcinoma or lung carcinoma, though many other malignancies can give rise to cerebral metastases. +Primary brain lesions are rare and range from benign tumors to extremely aggressive lesions with a poor prognosis. These tumors arise from the different cell lines and include gliomas, oligodendrocytomas, and choroid plexus tumors. Primary brain tumors may occur at any age, though there is a small peak incidence in the first few years of life followed by a later peak in early to middle age. +Regional Anatomy • Brain and Its Blood Supply 8 + + + +BRAIN AND ITS BLOOD SUPPLY Brain +The brain is a component of the central nervous system. During development the brain can be divided into five +continuous parts (Figs. 8.36 and 8.37). From rostral (or cranial) to caudal they are: + +of the brainstem. (However, in common usage today, the term brainstem usually refers to the midbrain, pons, and medulla.) +■ The mesencephalon (midbrain), which is the first part of the brainstem seen when an intact adult brain is examined, spans the junction between the middle and posterior cranial fossae. +■ The metencephalon, which gives rise to the cerebel- + + + +■ The telencephalon (cerebrum) becomes the large cerebral hemispheres. The surface of these hemispheres consists of elevations (gyri) and depressions (sulci), and the hemispheres are partially separated by a deep longi-tudinal fissure. The cerebrum fills the area of the cranial cavity above the tentorium cerebelli and is subdivided + +lum (consisting of two lateral hemispheres and a midline part in the posterior cranial fossa below the tentorium cerebelli) and the pons (anterior to the cerebellum, and is a bulging part of the brainstem in the most anterior part of the posterior cranial fossa against the clivus and dorsum sellae). + +into lobes based on position. ■ The myelencephalon (medulla oblongata), the + +■ The diencephalon, which is hidden from view in the adult brain by the cerebral hemispheres, consists of the thalamus, hypothalamus, and other related structures, and classically is considered to be the most rostral part + +caudalmost part of the brainstem, ends at the foramen magnum or the uppermost rootlets of the first cervical nerve and to which cranial nerves VI to XII are attached. + + + + + + + + + +Cerebral hemispheres (telencephalon) Parietal lobe + + + +Frontal lobe + +Occipital lobe + + + + + +Temporal lobe + + + + + + +Cerebellum (metencephalon) +Pons (metencephalon) + +Medulla oblongata (myelencephalon) + + + +Fig. 8.36 Lateral view of the brain. 867 +Head and Neck + + + +Telencephalon + + + + + + + + +Thalamus Diencephalon +Hypothalamus + + + +Cerebellum (metencephalon) + +Midbrain (mesencephalon) + +Pons (metencephalon) + +Medulla oblongata (myelencephalon) + + +Fig. 8.37 Sagittal section of the brain. + + + + + + +Blood supply +The brain receives its arterial supply from two pairs of vessels, the vertebral and internal carotid arteries (Fig. 8.38), which are interconnected in the cranial cavity to produce a cerebral arterial circle (of Willis). + + +The two vertebral arteries enter the cranial cavity through the foramen magnum and just inferior to the pons fuse to form the basilar artery. +The two internal carotid arteries enter the cranial cavity through the carotid canals on either side. + + + + + + + + + + + + + + + + + + + +868 + +Anterior cerebral Middle cerebral + +Ophthalmic +Posterior cerebral + +Anterior communicating + +Cerebral arterial circle + + +Posterior communicating + + +Fig. 8.38 Arterial supply to the brain. A. Diagram. B. Magnetic resonance angiogram showing normal carotid and vertebral arteries. C. Enhanced CT scan of carotid vessels. + + +Basilar + + + +Right internal carotid + + +Left internal carotid + + + + + + + +Right common carotid + + + +Right vertebral + + + +Right subclavian + +Brachiocephalic +Aortic arch +A + +Left vertebral + + + +Left subclavian + +Left common carotid + + + +Basilar + + + + + + + + + + +Right internal carotid + + + + + +Right vertebral + + + + +Left internal carotid + +Left vertebral + +Left common carotid + + +Right internal carotid + +Right vertebral + + + +Right common carotid + +Left internal carotid + + + + +Left vertebral + + +Left common carotid + + +Right common carotid + + +869 B C +Head and Neck + + + + +Vertebral arteries +Each vertebral artery arises from the first part of each subclavian artery (Fig. 8.38) in the lower part of the neck, and passes superiorly through the foramen transver-sarium of the upper six cervical vertebrae. On entering the + +■ A third branch joins with its companion from the other side to form the single anterior spinal artery, which then descends in the anterior median fissure of the spinal cord. + +The basilar artery travels in a rostral direction along the + +cranial cavity through the foramen magnum each verte-bral artery gives off a small meningeal branch. +Continuing forward, the vertebral artery gives rise to three additional branches before joining with its companion vessel to form the basilar artery (Figs. 8.38 and 8.39): + + +anterior aspect of the pons (Fig. 8.39). Its branches in a caudal to rostral direction include the anterior inferior cerebellar arteries, several small pontine arteries, and the superior cerebellar arteries. The basilar artery ends as a bifurcation, giving rise to two posterior cerebral arteries. + + + +■ The first is a posterior inferior cerebellar artery. +■ A second branch is the posterior spinal artery, which passes posteriorly around the medulla and then descends on the posterior surface of the spinal cord in the area of the attachment of the posterior roots—there are two posterior spinal arteries, one on each side (although the posterior spinal arteries can originate directly from the vertebral arteries, they more commonly branch from the posterior inferior cerebellar arteries). + +Internal carotid arteries +The two internal carotid arteries arise as one of the two terminal branches of the common carotid arteries (Fig. 8.38). They proceed superiorly to the base of the skull where they enter the carotid canal. +Entering the cranial cavity each internal carotid artery gives off the ophthalmic artery, the posterior com-municating artery, the middle cerebral artery, and the anterior cerebral artery (Fig. 8.39). + + + + + + + + + + + +Frontal lobe + + + + +Temporal lobe + +Middle cerebral Posterior communicating Posterior cerebral +Pons + + + + +Anterior spinal + +Vertebral + +Cerebellum + +Anterior cerebral + + +Anterior communicating Anterior cerebral + +Midbrain +Superior cerebellar Basilar +Anterior inferior cerebellar + + + +Posterior inferior cerebellar + +Posterior spinal + + + + +870 Fig. 8.39 Arteries on the base of the brain. +Regional Anatomy • Brain and Its Blood Supply 8 + + + + +Cerebral arterial circle +The cerebral arterial circle (of Willis) is formed at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels (Fig. 8.38). This anasto-motic interconnection is accomplished by: + +■ an anterior communicating artery connecting the left and right anterior cerebral arteries to each other, and +■ two posterior communicating arteries, one on each side, connecting the internal carotid artery with the posterior cerebral artery (Figs. 8.38 and 8.39). + + + + + + + +In the clinic + +Stroke +A stroke, or cerebrovascular accident (CVA), is defined as the interruption of blood flow to the brain or brainstem resulting in impaired neurological function lasting more than 24 hours. Neurological impairment resolving within 24 hours is known as a transient ischemic attack (TIA) or mini-stroke. Based on their etiology, strokes are broadly classified as either ischemic or hemorrhagic. Ischemic strokes are further divided into those caused by thrombotic or embolic phenomena. The latter is by far the commonest type of stroke and is often caused by emboli that originate from atherosclerotic plaques in the carotid arteries that migrate into and block smaller intracranial vessels. Hemorrhagic strokes are caused by rupture of blood vessels. +The risk factors for stroke are those of cardiovascular disease, such as diabetes, hypertension, and smoking. In younger patients underlying clotting disorders, use of oral contraceptives, and illicit substance abuse (such as cocaine) are additional causes. +The symptoms and signs of a stroke depend on the distribution of impaired brain perfusion. Common presentations include rapid-onset hemiparesis or hemisensory loss, visual field deficits, dysarthria, ataxia, and a decreased level of consciousness. +Stroke is a neurological emergency. It is therefore important to establish the diagnosis as early as possible so that urgent and potentially life-saving treatment can be administered. Potent thrombolytic (blood-thinning) drugs can restore cerebral blood flow and improved patient outcome if administered within 3 to 4.5 hours of onset of the patient’s symptoms. +Following initial clinical history taking and neurological examination, all patients with suspected stroke should undergo urgent brain imaging with computed tomography (CT). This is to identify hemorrhagic strokes for which thrombolytic therapy is contraindicated and to exclude an alternative diagnosis such as malignancy. In ischemic stroke, early CT imaging may appear normal or can show a relatively darker area of low density that corresponds to the region of abnormal brain perfusion. Due to subsequent brain + + + +edema and swelling, the affected brain also loses its normal sulcal pattern (Fig. 8.40A). If thrombolysis is performed, a +24-hour follow-up CT scan is routinely carried out to evaluate for complications such as intracranial hemorrhage. +Additional diagnostic workup of stroke includes hematological and biochemical blood tests to identify causes such as hypoglycemia or underlying clotting disorders. A toxicology screen may be useful to identify substance intoxication, which can mimic stroke. +The full extent of neurological injury can be evaluated on subsequent magnetic resonance imaging (MRI) of the brain, which has better soft tissue resolution compared to CT. MRI is also useful for identifying strokes that may be too small to detect on a CT scan. MRI scans are produced by using complicated algorithms that create a series of images, also known as sequences. Various sequences can be obtained to assess different anatomical and physiological properties of the brain. A stroke, whether acute or chronic, will appear as a bright region on a sequence that is sensitive to fluid (T2 weighted) (Fig. 8.40B). To identify whether a stroke is acute, further sequences are obtained, known as diffusion-weighted imaging (DWI) (Fig. 8.40C) and the apparent diffusion coefficient (ADC) (Fig. 8.40D) map. These evaluate the diffusion of water molecules in the brain. If the region of abnormality appears bright on the DWI sequence and dark on the ADC map, this is known as restricted diffusion, which is compatible with an acute stroke. These changes can persist for up to a week after the initial insult. +Imaging of the carotid and vertebral arteries is also performed to assess for any treatable atherosclerotic changes and stenosis. This can be done with ultrasound, CT, or less frequently, MRI. +Management of a stroke is multidisciplinary. Supportive treatment to stabilize the patient is a priority. Stroke specialists, speech and language therapists, occupational therapists, and physiotherapists have key roles in patient rehabilitation. Long-term use of antiplatelet drugs such as aspirin and modification of cardiovascular disease risk factors are important in the secondary prevention of stroke. +(continues) + + + +871 +Head and Neck + + +In the clinic—cont’d + + + + + + + + + + + + + + + + + + + + + +A B + + + + + + + + + + + + + + + + + + + + + +C D + +Fig. 8.40 Different imaging modalities used to evaluate a stroke (arrows). A. CT scan. B. T2- weighted CT. C. Diffusion-weighted image (DWI). D. Apparent diffusion coefficient image (ADC). + + + + + + +872 +Regional Anatomy • Brain and Its Blood Supply 8 + + + +In the clinic + +Endarterectomy +Endarterectomy is a surgical procedure to remove atheromatous plaque from arteries. +Atheromatous plaques occur in the subendothelial layer of vessels and consist of lipid-laden macrophages and cholesterol debris. The developing plaque eventually accumulates fibrous connective tissue and calcifies. Plaque + + + +In the clinic + +Intracerebral aneurysms +Cerebral aneurysms arise from the vessels in and around the cerebral arterial circle (of Willis). They typically occur in and around the anterior communicating artery, the posterior communicating artery, the branches of the middle cerebral artery, the distal end of the basilar artery (Fig. 8.41), and the posterior inferior cerebellar artery. +As the aneurysms enlarge, they have a significant risk of rupture. Typically patients have no idea that there is anything wrong. As the aneurysm ruptures, the patient complains of a sudden-onset “thunderclap” headache that produces neck stiffness and may induce vomiting. In a number of patients death ensues, but many patients reach the hospital, where the diagnosis is established. An initial CT + + + +commonly occurs around vessel bifurcations, limiting blood flow, and may embolize to distal organs. +During endarterectomy, plaque is removed and the vessel reopened. In many instances a patch of material is sewn over the hole in the vessel, enabling improved flow and preventing narrowing from the suturing of the vessel. + + + + +scan demonstrates blood within the subarachnoid space, and this may be associated with an intracerebral bleed. Further management usually includes cerebral angiography, which enables the radiologist to determine the site, size, and origin of the aneurysm. +Usually patients undergo complex surgery to ligate the neck of the aneurysm. More recently radiological intervention has superseded the management of some aneurysms in specific sites. This treatment involves cannulation of the femoral artery, and placement of a long catheter through the aorta into the carotid circulation and thence into the cerebral circulation. The tip of the catheter is placed within the aneurysm and is packed with fine microcoils (Fig. 8.42), which seals the rupture. + + + + +Anterior + + + + + + + + + + + + + + + + + + + + +A + +Aneurysm Basilar tip artery aneurysm + + + + + + + + + + + + + + + + + + + + +B + +Posterior + + +Fig. 8.41 Basilar tip aneurysm. A. Three-dimensional cranial cutaway CT scan. B. Magnified view of aneurysm. +(continues) 873 +Head and Neck + + + +In the clinic—cont’d + +Left and right cerebral arteries + + + + + + + + + + + + + + + +A + + + +Left anterior cerebral artery + + + + + + + + + + + + + + + +B + + + +Anterior communicating artery aneurysm + +Left internal carotid artery + +Middle cerebral artery + +Anterior communicating artery aneurysm after it has been sealed + + +Fig. 8.42 Anterior communicating aneurysm. A. Left carotid angiogram. B. Left carotid angiogram after embolization. + + + + + +Venous drainage Emissary vein +Venous drainage of the brain begins internally as networks + + +Diploic vein + +Dura mater + +of small venous channels lead to larger cerebral veins, Cerebral vein Dural venous sinus Skull cerebellar veins, and veins draining the brainstem, which +eventually empty into dural venous sinuses. The dural venous sinuses are endothelial-lined spaces between the outer periosteal and the inner meningeal layers of the dura mater, and eventually lead to the internal jugular veins. Also emptying into the dural venous sinuses are diploic veins, which run between the internal and external tables of compact bone in the roof of the cranial cavity, and emissary veins, which pass from outside the cranial +cavity to the dural venous sinuses (Fig. 8.43). +The emissary veins are important clinically because they can be a conduit through which infections can enter the cranial cavity because they have no valves. + +Dural venous sinuses +The dural venous sinuses include the superior sagittal, inferior sagittal, straight, transverse, sigmoid, and occipital + +sinuses, the confluence of sinuses, and the cavernous, sphenoparietal, superior petrosal, inferior petrosal, and basilar sinuses (Fig. 8.44, Table 8.3). + + +Dural partition Pia mater +Subarachnoid space Arachnoid mater + +Fig. 8.43 Dural venous sinuses. + +874 +Regional Anatomy • Brain and Its Blood Supply 8 + + + +Inferior sagittal sinus +Superior sagittal sinus + + +Straight sinus + +Confluence of sinuses + + + +Great cerebral vein + + +Sigmoid sinus +Superior petrosal sinus + + + +Basilar sinus + + + +Sphenoparietal sinus + + +Intercavernous sinus + + +Ophthalmic vein + +Right transverse sinus + +Sigmoid sinus Superior petrosal sinus + + +Inferior petrosal sinus + +Cavernous sinus Pterygoid plexus of veins + +Fig. 8.44 Veins, meninges, and dural venous sinuses. + + + +Table 8.3 Dural venous sinuses + + +Dural sinus Superior sagittal Inferior sagittal Straight + + +Occipital +Confluence of sinuses Transverse (right and left) + + + +Sigmoid (right and left) + + +Cavernous (paired) + +Intercavernous Sphenoparietal (paired) Superior petrosal (paired) Inferior petrosal (paired) + +Basilar + +Location +Superior border of falx cerebri Inferior margin of falx cerebri +Junction of falx cerebri and tentorium cerebelli + + +In falx cerebelli against occipital bone +Dilated space at the internal occipital protuberance +Horizontal extensions from the confluence of sinuses along the posterior and lateral attachments of the tentorium cerebelli + +Continuation of transverse sinuses to internal jugular vein; groove of parietal, temporal, and occipital bones +Lateral aspect of body of sphenoid + +Crossing sella turcica +Inferior surface of lesser wings of sphenoid Superior margin of petrous part of temporal bone +Groove between petrous part of temporal bone and occipital bone ending in internal jugular vein +Clivus, just posterior to sella turcica of sphenoid + +Receives +Superior cerebral, diploic, and emissary veins and CSF A few cerebral veins and veins from the falx cerebri +Inferior sagittal sinus, great cerebral vein, posterior cerebral veins, superior cerebellar veins, and veins from the falx cerebri +Communicates inferiorly with vertebral plexus of veins Superior sagittal, straight, and occipital sinuses +Drainage from confluence of sinuses (right—transverse and usually superior sagittal sinuses; left—transverse and usually straight sinuses); also superior petrosal sinus, and inferior cerebral, cerebellar, diploic, and emissary veins +Transverse sinuses, and cerebral, cerebellar, diploic, and emissary veins + +Cerebral and ophthalmic veins, sphenoparietal sinuses, and emissary veins from pterygoid plexus of veins +Interconnect cavernous sinuses Diploic and meningeal veins +Cavernous sinus, and cerebral and cerebellar veins +Cavernous sinus, cerebellar veins, and veins from the internal ear and brainstem +Connect bilateral inferior petrosal sinuses and +communicate with vertebral plexus of veins 875 +Head and Neck + + + + +Superior sagittal sinus +The superior sagittal sinus is in the superior border of the falx cerebri (Fig. 8.44). It begins anteriorly at the foramen cecum, where it may receive a small emissary vein from the nasal cavity, and ends posteriorly in the confluence of sinuses, usually bending to the right to empty into the right transverse sinus. The superior sagittal sinus communicates with lateral extensions (lateral lacunae) of the sinus con-taining numerous arachnoid granulations. +The superior sagittal sinus usually receives cerebral veins from the superior surface of the cerebral hemispheres, diploic and emissary veins, and veins from the falx cerebri. + +Inferior sagittal and straight sinuses +The inferior sagittal sinus is in the inferior margin of the falx cerebri (Fig. 8.44). It receives a few cerebral veins and veins from the falx cerebri, and ends posteriorly at the anterior edge of the tentorium cerebelli, where it is joined by the great cerebral vein and together with the great + +and occipital bones, before ending at the beginning of the internal jugular veins. The sigmoid sinuses also receive blood from cerebral, cerebellar, diploic, and emissary veins. + +Cavernous sinuses +The paired cavernous sinuses are against the lateral aspect of the body of the sphenoid bone on either side of the sella turcica (Figs. 8.45 and 8.46). They are of great clinical importance because of their connections and the struc-tures that pass through them. +The cavernous sinuses receive blood not only from cerebral veins but also from the ophthalmic veins (from the orbit) and emissary veins (from the pterygoid plexus of veins in the infratemporal fossa). These connections provide pathways for infections to pass from extracranial sites into intracranial locations. In addition, because struc-tures pass through the cavernous sinuses and are located in the walls of these sinuses they are vulnerable to injury due to inflammation. +Structures passing through each cavernous sinus are: + + + +cerebral vein forms the straight sinus (Fig. 8.44). +The straight sinus continues posteriorly along the junc-tion of the falx cerebri and the tentorium cerebelli and ends in the confluence of sinuses, usually bending to the left to + + +■ the internal carotid artery, and ■ the abducent nerve [VI]. + + + +empty into the left transverse sinus. +The straight sinus usually receives blood from the infe-rior sagittal sinus, cerebral veins (from the posterior part of the cerebral hemispheres), the great cerebral vein + + +Trochlear nerve [IV] Abducent nerve [VI] + +Internal carotid artery + +Oculomotor nerve [III] + + + +(draining deep areas of the cerebral hemispheres), superior cerebellar veins, and veins from the falx cerebri. + +Confluence of sinuses, transverse and sigmoid sinuses +The superior sagittal and straight sinuses, and the occipital sinus (in the falx cerebelli) empty into the confluence of sinuses, which is a dilated space at the internal occipital protuberance (Fig. 8.44) and is drained by the right and left transverse sinuses. +The paired transverse sinuses extend in horizontal directions from the confluence of sinuses where the tento-rium cerebelli joins the lateral and posterior walls of the cranial cavity. +The right transverse sinus usually receives blood from the superior sagittal sinus and the left transverse sinus usually receives blood from the straight sinus. +The transverse sinuses also receive blood from the superior petrosal sinus, veins from the inferior parts of the + + +Pituitary gland Dura mater + +Diaphragma sellae + + + + + + + + + + + + + + + +Sphenoidal (paranasal) sinuses + +Cavernous (venous) sinuses + + + +cerebral hemispheres and the cerebellum, and diploic and emissary veins. +As the transverse sinuses leave the surface of the occipital bone, they become the sigmoid sinuses (Fig. 8.44), +876 which turn inferiorly, grooving the parietal, temporal, + + +Ophthalmic division of trigeminal nerve [V1] + +Maxillary division of trigeminal nerve [V2] + +Fig. 8.45 Cavernous sinuses. +Regional Anatomy • Brain and Its Blood Supply 8 + + + +Oculomotor nerve [III] + +Abducent nerve [VI] + +Posterior clinoid process + +Infundibulum (stalk of pituitary gland) + + + + + + + + + +Optic nerve [III] + + +Trochlea nerve [IV] + + + +Tentorium cerebelli + +Trigeminal nerve [V] + +Anterior clinoid process + +Oculomotor nerve [III] + +Trochlea nerve [IV] + +Ophthalmic nerve [V1] + + +Abducent nerve [VI] + +Maxillary nerve [V2] + + + + +Trigeminal ganglion + +Mandibular nerve [V3] + +Internal carotid artery + +Cut edge of dura mater + + +Fig. 8.46 Lateral view of right cavernous sinus with meningeal layer of dura removed to show contents. + + + + + +Structures in the lateral wall of each cavernous sinus are, from superior to inferior: + +begins at the posterior end of the cavernous sinus, passes posterolaterally along the superior margin of the petrous + + + + +■ the oculomotor nerve [III], ■ the trochlear nerve [IV], +■ the ophthalmic nerve [V1], and ■ the maxillary nerve [V2]. + +Connecting the right and left cavernous sinuses are the + +part of each temporal bone, and connects to the transverse sinus (Fig. 8.44). The superior petrosal sinuses also receive cerebral and cerebellar veins. +The inferior petrosal sinuses also begin at the posterior ends of the cavernous sinuses. These bilateral sinuses pass posteroinferiorly in a groove between the petrous part of the temporal bone and the basal part of the occipital bone, + + + +intercavernous sinuses on the anterior and posterior sides of the pituitary stalk (Fig. 8.44). +Sphenoparietal sinuses drain into the anterior ends of each cavernous sinus. These small sinuses are along the inferior surface of the lesser wings of the sphenoid and receive blood from the diploic and meningeal veins. + +Superior and inferior petrosal sinuses +The superior petrosal sinuses drain the cavernous sinuses into the transverse sinuses. Each superior petrosal sinus + +ending in the internal jugular veins. They assist in draining the cavernous sinuses and also receive blood from cerebel-lar veins and veins from the internal ear and brainstem. +Basilar sinuses connect the inferior petrosal sinuses to each other and to the vertebral plexus of veins. They are on the clivus, just posterior to the sella turcica of the sphenoid bone (Fig. 8.44). + + +877 +Head and Neck + + +In the clinic + +Scalp and meninges +Summary of relationships and clinical significance of the scalp and meninges (Fig. 8.47). + + +Connected together as a structural unit + +Connective tissue: contains major nerves and vessels of the scalp +Aponeurosis Skin + + + +Superior sagittal sinus + +Diploic vein +Neurovascular bundle + + + +Emissary vein: can spread infection from the scalp into the cranial cavity + +3 + + +Subdural hematoma + + + +1 Periosteum +Extradural hematoma + +Fracture + + +2 + + + + + + + + + + +III IV + +V1 VI V2 +Arachnoid + + +Diploë Outer +Inner table table + +Bone + + + +Subarachnoid space Pia +Anterior cerebral artery + + + +Cavernous sinus +Optic tracts + + + +Internal carotid +artery 4 + + +Periostial layer Meningeal layer + + +Dura + + +1 Loose connective tissue (danger area) +• In scalping injuries, this is the layer in which separation occurs. • Infection can easily spread in this layer. +• Blunt trauma can result in hemorrhage in this layer (blood can spread forward into the face, resulting in “black eyes”). +2 Rupture of the middle meningeal artery (branches) by fracture of the inner table of bone +results in extradural hematoma. Under pressure, the blood progressively separates dura from the bone. +3 Tear to cerebral vein where it crosses dura to enter cranial venous sinus can result in subdural hematoma. The tear separates a thin layer of meningeal dura from that which remains attached to the periosteal layer. As a result, the hematoma is covered by an inner limiting membrane derived from part of the meningeal dura. + +4 Aneurysm +• Ruptured aneurysms of vessels of the cerebral arterial circle hemorrhage directly into the subarachnoid space and CSF. 878 Fig. 8.47 Scalp and meninges. +Regional Anatomy • Brain and Its Blood Supply 8 + + + +In the clinic + +Head injury +Head trauma is a common injury and is a significant cause of morbidity and death. Head injury may occur in isolation, but often the patient has other injuries; it should always be suspected in patients with multiple injuries. Among patients with multiple trauma, 50% die from the head injury. +At the time of the initial head injury two processes take place. + +■ First the primary brain injury may involve primary axonal and cellular damage, which results from the shearing + + + +deceleration forces within the brain. These injuries are generally not repairable. Further primary brain injuries include intracerebral hemorrhage and penetrating injuries, which may directly destroy gray and white matter. +■ The secondary injuries are sequelae of the initial trauma. They include scalp laceration, fracture of the cranial vault, disruption of intracerebral arteries and veins, intracerebral edema, and infection. In most cases these can be treated if diagnosed early, and rapid and effective treatment will significantly improve the patient’s recovery and prognosis. + + + + + + + + +In the clinic + +Types of intracranial hemorrhage Extradural hematoma Shift of the falx cerebri Primary brain hemorrhage +The many causes of a primary brain hemorrhage include aneurysm rupture, hypertension (intracerebral hematoma secondary to high blood pressure), and bleeding after cerebral infarction. +Extradural hemorrhage +An extradural hemorrhage (Fig. 8.48) is caused by arterial damage and results from tearing of the branches of the middle meningeal artery, which typically occurs in the region of the pterion. Blood collects between the periosteal layer of the dura and the calvaria and under arterial pressure slowly expands. +The typical history is of a blow to the head (often during a sporting activity) that produces a minor loss of consciousness. Following the injury the patient usually regains consciousness and has a lucid interval for a period of hours. After this, rapid drowsiness and unconsciousness ensue, which may lead to death. + + + + + + + +Fig. 8.48 Extradural hematoma. Axial CT scan of brain. +(continues) + + + + + +879 +Head and Neck + + + +In the clinic—cont’d + +Subdural hematoma +A subdural hematoma (Fig. 8.49) results from venous bleeding, usually from torn cerebral veins where they enter the superior sagittal sinus. The tear and resulting seepage of blood separates the thin layer of dural border cells from the rest of the dura as the hematoma develops. +Patients at most risk of developing a subdural hematoma are the young and elderly. The increased CSF space in patients with cerebral atrophy results in a greater than normal stress on the cerebral veins entering the sagittal + + +Lateral ventricles shifted + + + +sinus. The clinical history usually includes a trivial injury followed by an insidious loss of consciousness or alteration of personality. +Subarachnoid hemorrhage +Subarachnoid hemorrhage (Fig. 8.50) may occur in patients who have undergone significant cerebral trauma, but typically it results from a ruptured intracerebral aneurysm arising from the vessels supplying and around the arterial circle (of Willis). + + +Subarachnoid basal cisterns containing blood + + + + + + + + + + + + + + + + + + + + + + + +Subdural hematoma + +Fig. 8.49 Chronic (low-density) subdural hematoma. Axial CT scan of brain. +Fig. 8.50 Subarachnoid hemorrhage. Axial CT scan of brain. + + + + + + + + + + + + + + +880 +Regional Anatomy • Brain and Its Blood Supply 8 + + + +In the clinic + +Tuberculosis of the central nervous system Tuberculosis (TB) may invade the central nervous system, including the brain, spinal cord, and meninges (Fig. 8.51). Symptoms of brain TB include headache, neck stiffness, weight loss, and fever. Symptoms of spinal cord TB include leg weakness and fecal and urinary incontinence. Meningitis can cause altered mental status, fever, and seizures. Treatment usually requires a cocktail of drugs for 1 year, but treatment for brain TB can require 2 years. + + + + + + + + + + + + + + + + + + + + + + + + + + + +Fig. 8.51 MRI of the brain shows peripherally enhancing tuberculosis lesions in the left temporal lobe and cerebral peduncle. + + + + + + + + +In the clinic + +Emissary veins +Emissary veins connect extracranial veins with intracranial veins and are important clinically because they can be a conduit through which infections can enter the cranial cavity. Emissary veins lack valves, as do the majority of veins in the head and neck. + +In the clinic + +Concussion +Concussion (mild traumatic brain injury [MTBI]) is the most common type of traumatic brain injury. The injury typically results from a rapid deceleration of the head or by a rotation of the brain within the cranial cavity. General symptoms of MTBI can include posttraumatic amnesia, confusion, loss of consciousness, headache, dizziness, vomiting, lack of motor coordination, and light sensitivity. The diagnosis of concussion, MTBI, is based on the event, the current neurological status, and the state of consciousness of the patient. + + + +In the clinic + +Clinical assessment of patients with head injury Clinical assessment of patients with head injury always appears relatively straightforward. In reality it is usually far from straightforward. +Patients may have a wide spectrum of modes of injury from a simple fall to complex multiple trauma. The age of the patient and ability to communicate about the injuries are important factors. +The circumstances in which the injury may have occurred should be documented because some head injuries result from a serious assault, and the physician may be required to give evidence to a court of law. +Determining the severity of head injury may be difficult because some injuries occur as a result of or in association with alcohol intoxication. +Even when the diagnosis has been made and the correct management has been instigated, the circumstances in which the injury occurred and the environment to which the patient will return after treatment need to be reviewed to prevent further injuries (e.g., an elderly person tripping on loose carpet on a staircase). +A thorough clinical examination includes all systems, but with a special focus on the central and peripheral nervous systems. The level of consciousness must also be assessed and accurately documented using the Glasgow Coma Scale, which allows clinicians to place a numerical value upon the level of consciousness so that any deterioration or improvement can be measured and quantified. +Glasgow Coma Scale +The Glasgow Coma Scale was proposed in 1974 and is now widely accepted throughout the world. There is a total score of 15 points, such that 15/15 indicates that the patient is alert and fully oriented, whereas 3/15 indicates a severe and deep coma. The points score comprises a best motor response (total of 6 points), best verbal response (total of 5 points), and best eye movement response (total of 4 +points). 881 +Head and Neck + + + +In the clinic + +Treatment of head injury +Treatment of primary brain injury is extremely limited. Axonal disruption and cellular death are generally irrecoverable. Whenever the brain is injured, like most tissues, it swells. Because the brain is encased within a fixed space (the skull), swelling impairs cerebral function and has two other important effects. + +■ First, the swelling compresses the blood supply into the skull, resulting in a physiologically dramatic increase in blood pressure. +■ Second, the cerebral swelling may be diffuse, eventually squeezing the brain and brainstem through the foramen magnum (coning). This compression and disruption of the + + + +brainstem may lead to a loss of basic cardiorespiratory function, and death will ensue. Focal cerebral edema may cause one side of the brain to herniate beneath the falx cerebri (falcine herniation). + +Simple measures to prevent the swelling include hyperventilation (which alters the intracerebral acid–base balance and decreases swelling) and intravenous corticosteroids (though their action is often delayed). +Extracerebral hematoma may be removed surgically. The outcome of patients with head injury depends on +how the secondary injury is managed. Even with a severe primary injury, patients may recover to lead a normal life. + + + + + + + +In the clinic + +Increased intracranial pressure and coning +The skull is a closed bony compartment, and the brain and cerebrospinal fluid are maintained physiologically within a narrow intracranial pressure range. Any new space-occupying lesion, such as a hematoma, an injury that leads to brain swelling, or a brain tumor, can increase intracranial pressure and compress the brain. In severe cases, the brain may be squeezed down into the foramen magnum, giving it a cone shape, termed cerebral herniation, or “coning.” This may in turn compress the brainstem and upper cervical spinal cord, which can be fatal. +Congenital herniation or coning of the cerebellar tonsils through the foramen magnum can also occur if the posterior fossa is too small, a condition known as Chiari I malformation (Fig. 8.52). This often causes no problems in childhood and may only start causing symptoms in adulthood. + + + + +Cerebellar tonsillar descent + +Fig. 8.52 MRI of the brain reveals an incidental Chiari I malformation with herniation of the the cerebellar tonsils through the foramen magnum, giving rise to a cone shape. + + + + + +882 +Regional Anatomy • Cranial Nerves 8 + + + +CRANIAL NERVES + +The 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and pass through foramina or fis-sures in the cranial cavity. All nerves except one, the acces-sory nerve [XI], originate from the brain. +In addition to having somatic and visceral components similar to those of spinal nerves, some cranial nerves also contain special sensory and motor components (Tables 8.4 and 8.5). + +The special sensory components are associated with hearing, seeing, smelling, balancing, and tasting. +Special motor components include those that innervate skeletal muscles derived embryologically from the pharyn-geal arches and not from somites. +In human embryology, six pharyngeal arches are desig-nated, but the fifth pharyngeal arch never develops. Each of the pharyngeal arches that does develop is associated with a developing cranial nerve or one of its branches. + + +Table 8.4 Cranial nerve functional components + + +Functional component General somatic afferent + +General visceral afferent Special afferent* + + +General somatic efferent + +General visceral efferent + +Branchial efferent** + +Abbreviation GSA + +GVA SA + + +GSE + +GVE + +BE + +General function +Perception of touch, pain, temperature + +Sensory input from viscera +Smell, taste, vision, hearing, and balance + + +Motor innervation to skeletal (voluntary) muscles +Motor innervation to smooth muscle, heart muscle, and glands +Motor innervation to skeletal muscles derived from pharyngeal arch mesoderm + +Cranial nerves containing component +Trigeminal nerve [V]; facial nerve [VII]; glossopharyngeal nerve [IX]; vagus nerve [X] +Glossopharyngeal nerve [IX]; vagus nerve [X] +Olfactory nerve [I]; optic nerve [II]; facial nerve [VII]; vestibulocochlear nerve [VIII]; glossopharyngeal nerve [IX]; vagus nerve [X] +Oculomotor nerve [III]; trochlear nerve [IV]; abducent nerve [VI]; hypoglossal nerve [XII] +Oculomotor nerve [III]; facial nerve [VII]; glossopharyngeal nerve [IX]; vagus nerve [X] +Trigeminal nerve [V]; facial nerve [VII]; glossopharyngeal nerve [IX]; vagus nerve [X]; accessory nerve [XI] (see Diogo R et al. Nature 2015;520:466–473) + +Other terminology used when describing functional components: +*Special sensory, or special visceral afferent (SVA): smell, taste. Special somatic afferent (SSA): vision, hearing, balance. **Special visceral efferent (SVE) or branchial motor. + + +Table 8.5 Cranial nerves (see Table 8.4 for abbreviations) + +COMPONENT + +Nerve +Olfactory nerve [I] Optic nerve [II] Oculomotor nerve [III] + + + +Trochlear nerve [IV] +Trigeminal nerve [V] + +Afferent SA +SA + + + + + +GSA + +Efferent + + + +GSE, GVE + + + +GSE +BE + +Exit from skull +Cribriform plate of ethmoid bone Optic canal +Superior orbital fissure + + + +Superior orbital fissure +Superior orbital fissure— ophthalmic division [V1] Foramen rotundum—maxillary nerve [V2] +Foramen ovale—mandibular division [V3] + +Function Smell Vision +GSE—innervates levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique muscles GVE—innervates sphincter pupillae for pupillary constriction; ciliary muscles for accommodation of the lens for near vision +Innervates superior oblique muscle +GSA—sensory from: ophthalmic division [V1]—eyes, conjunctiva, orbital contents, nasal cavity, frontal sinus, ethmoidal cells, upper eyelid, dorsum of nose, anterior part of scalp, dura in anterior cranial fossa, superior part of tentorium cerebelli; maxillary nerve [V2]—dura in middle cranial fossa, nasopharynx, palate, nasal cavity, upper teeth, maxillary sinus, skin covering the side of the nose, lower eyelid, cheek, upper lip; mandibular division [V3]—skin of lower face, cheek, lower lip, anterior part of external ear, part of external acoustic meatus, temporal fossa, anterior two-thirds of tongue, lower teeth, mastoid air cells, mucous membranes of cheek, mandible, dura in middle cranial fossa +BE—innervates temporalis, masseter, medial and lateral pterygoids, tensor tympani, tensor veli palatini, anterior belly of +digastric, and mylohyoid muscles 883 +Continued +Head and Neck + + +Table 8.5 Cranial nerves (see Table 8.4 for abbreviations)—cont’d + +COMPONENT + +Nerve +Abducent nerve [VI] Facial nerve [VII] + + + + + + + +Vestibulocochlear nerve [VIII] +Glossopharyngeal nerve [IX] + + + + + +Vagus nerve [X] + + + + + + + + + + +Accessory nerve [XI] + +Afferent + + +GSA, SA + + + + + + + +SA + +GVA, SA, GSA + + + + + +GSA, GVA, SA + +Efferent GSE GVE, BE + + + + + + + + + +GVE, BE + + + + + +GVE, BE + + + + + + + + + + +BE + +Exit from skull Superior orbital fissure +Stylomastoid foramen (nerve leaves cranial cavity through internal acoustic meatus and gives rise to branches in the facial canal of the temporal bone prior to exiting through the stylomastoid foramen; these branches leave the skull through other fissures and canals.) +(Nerve leaves cranial cavity through internal acoustic meatus) +Jugular foramen + + + + + +Jugular foramen + + + + + + + + + + +Jugular foramen + +Function +Innervates lateral rectus muscle +GSA—sensory from part of external acoustic meatus and deeper parts of auricle +SA—taste from anterior two-thirds of tongue +GVE—innervates lacrimal gland, submandibular and sublingual salivary glands, and mucous membranes of nasal cavity, hard and soft palates +BE—innervates muscles of face (muscles of facial expression) and scalp derived from the second pharyngeal arch, and stapedius, posterior belly of digastric, stylohyoid muscles +Vestibular division—balance Cochlear division—hearing +GVA—sensory from carotid body and sinus +GSA—posterior one-third of tongue, palatine tonsils, oropharynx, and mucosa of middle ear, pharyngotympanic tube, and mastoid air cells +SA—taste from posterior one-third of tongue GVE—innervates parotid salivary gland +BE—innervates stylopharyngeus muscle +GSA—sensory from larynx, laryngopharynx, deeper parts of auricle, part of external acoustic meatus, and dura in posterior cranial fossa +GVA—sensory from aortic body chemoreceptors and aortic arch baroreceptors, esophagus, bronchi, lungs, heart, and abdominal viscera of the foregut and midgut +SA—taste from the epiglottis and pharynx +GVE—innervates smooth muscle and glands in the pharynx, larynx, thoracic viscera, and abdominal viscera of the foregut and midgut +BE—innervates one tongue muscle (palatoglossus), muscles of soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx +Innervates sternocleidomastoid and trapezius muscles [for classification as BE see Diogo R et al. Nature 2015;520:466–473.] + +Hypoglossal nerve [XII] GSE Hypoglossal canal Innervates hyoglossus, genioglossus, and styloglossus muscles and all intrinsic muscles of the tongue + + + + + + + + + + + + + + + + + + + +884 +Regional Anatomy • Cranial Nerves 8 + + + +These cranial nerves carry efferent fibers that innervate the musculature derived from the pharyngeal arch. + +■ peripheral processes that act as receptors in the nasal mucosa, and + +Innervation of the musculature derived from the five pharyngeal arches that do develop is as follows: + +■ central processes that return information to the brain. + + + +■ first arch—trigeminal nerve [V3], ■ second arch—facial nerve [VII], +■ third arch—glossopharyngeal nerve [IX], +■ fourth arch—superior laryngeal branch of the vagus nerve [X], +■ sixth arch—recurrent laryngeal branch of the vagus nerve [X], + + +The receptors are in the roof and upper parts of the nasal cavity, and the central processes, after joining into small bundles, enter the cranial cavity by passing through the cribriform plate of the ethmoid bone (Fig. 8.53). They terminate by synapsing with secondary neurons in the olfactory bulbs (Fig. 8.54). + + + +■ posterior arches—accessory nerve [XI]. + +Olfactory nerve [I] +The olfactory nerve [I] carries special afferent (SA) fibers + + +Optic nerve [II] +The optic nerve [II] carries SA fibers for vision. These fibers return information to the brain from photoreceptors + +for the sense of smell. Its sensory neurons have: in the retina. Neuronal processes leave the retinal + + + + + + + + + + + +Olfactory bulb + + + +Optic nerve [II] + +Oculomotor nerve [III] + +Abducent nerve [VI] Trochlear nerve [IV] + + + + + + +Trigeminal nerve [V] + + +Accessory nerve [XI] + + +Olfactory nerves [I] + + + + +Ophthalmic nerve [V1] Maxillary nerve [V2] +Mandibular nerve [V3] Trigeminal ganglion +Facial nerve [VII] + +Vestibulocochlear nerve [VIII] + + + + +Glossopharyngeal nerve [IX] Vagus nerve [X] +Hypoglossal nerve [XII] + + + + +Fig. 8.53 Cranial nerves exiting the cranial cavity. + + + + +885 +Head and Neck + + + + + + + +Olfactory bulbs + + + + +Temporal lobe + + + + +Pons + + + +Facial nerve [VII] + +Vestibulocochlear nerve [VIII] +Glossopharyngeal nerve [IX] + +Vagus nerve [X] with cranial root of accessory +Accessory nerve [XI] + +Optic nerve [II] + +Oculomotor nerve [III] + +Trochlear nerve [IV] + +Trigeminal nerve [V] sensory root +Trigeminal nerve [V] motor root +Abducent nerve [VI] + +Hypoglossal nerve [XII] + + +Cerebellum + + + + + +Fig. 8.54 Cranial nerves on the base of the brain. + + + + +receptors, join into small bundles, and are carried by the optic nerves to other components of the visual system in the brain. The optic nerves enter the cranial cavity through the optic canals (Fig. 8.53). + + +Oculomotor nerve [III] +The oculomotor nerve [III] carries two types of fibers: + +In the orbit, the GSE fibers in the oculomotor nerve innervate levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique muscles. The GVE fibers are preganglionic parasympathetic fibers that synapse in the ciliary ganglion and ultimately inner-vate the sphincter pupillae muscle, responsible for pupillary constriction, and the ciliary muscles, responsible for +accommodation of the lens for near vision. + + + +■ General somatic efferent (GSE) fibers innervate most of the extra-ocular muscles. +■ General visceral efferent (GVE) fibers are part of the parasympathetic part of the autonomic division of the PNS. + +The oculomotor nerve [III] leaves the anterior surface of + + +Trochlear nerve [IV] +The trochlear nerve [IV] is a cranial nerve that carries GSE fibers to innervate the superior oblique muscle, an extra-ocular muscle in the orbit. It arises in the midbrain and is the only cranial nerve to exit from the posterior surface of the brainstem (Fig. 8.54). After curving around + + + +the brainstem between the midbrain and the pons (Fig. 8.54). It enters the anterior edge of the tentorium cerebelli, continues in an anterior direction in the lateral wall of the cavernous sinus (Figs. 8.53 and 8.54; see Fig. 8.45), and +886 leaves the cranial cavity through the superior orbital fissure. + +the midbrain, it enters the inferior surface of the free edge of the tentorium cerebelli, continues in an anterior direc-tion in the lateral wall of the cavernous sinus (Figs. 8.53 and 8.54; see Fig. 8.45), and enters the orbit through the superior orbital fissure. +Regional Anatomy • Cranial Nerves 8 + + + +Trigeminal nerve [V] +The trigeminal nerve [V] is the major general sensory nerve of the head and also innervates muscles that move the lower jaw. It carries general somatic afferent (GSA) and branchial efferent (BE) fibers: + +Maxillary nerve [V2] +The maxillary nerve [V2] passes forward in the dura mater of the lateral wall of the cavernous sinus just inferior to the ophthalmic nerve [V1] (see Fig. 8.45), leaves the cranial cavity through the foramen rotundum (Fig. 8.53), and + + + + +■ The GSA fibers provide sensory input from the face, anterior one-half of the scalp, mucous membranes of the oral and nasal cavities and the paranasal sinuses, the nasopharynx, part of the ear and external acoustic meatus, part of the tympanic membrane, the orbital contents and conjunctiva, and the dura mater in the anterior and middle cranial fossae. +■ The BE fibers innervate the muscles of mastication; the tensor tympani, tensor veli palatini, and mylohyoid muscles; and the anterior belly of the digastric muscle. + +The trigeminal nerve exits from the anterolateral surface + +enters the pterygopalatine fossa. +The maxillary nerve [V2] receives sensory branches from the dura in the middle cranial fossa, the nasopharynx, the palate, the nasal cavity, teeth of the upper jaw, maxil-lary sinus, and skin covering the side of the nose, the lower eyelid, the cheek, and the upper lip. + + +Mandibular nerve [V3] +The mandibular nerve [V3] leaves the inferior margin of the trigeminal ganglion and leaves the skull through the foramen ovale (Fig. 8.53), and enters the infratemporal fossa. + + + +of the pons as a large sensory root and a small motor root (Fig. 8.54). These roots continue forward out of the poste-rior cranial fossa and into the middle cranial fossa by passing over the medial tip of the petrous part of the temporal bone (Fig. 8.53). +In the middle cranial fossa the sensory root expands into the trigeminal ganglion (Fig. 8.53), which contains cell bodies for the sensory neurons in the trigeminal nerve and is comparable to a spinal ganglion. The ganglion is in a depression (the trigeminal depression) on the anterior surface of the petrous part of the temporal bone, in a dural cave (the trigeminal cave). The motor root is below and completely separate from the sensory root at this point. +Arising from the anterior border of the trigeminal ganglion are the three terminal divisions of the trigeminal nerve, which in descending order are: + +The motor root of the trigeminal nerve also passes through the foramen ovale and unites with the sensory component of the mandibular nerve [V3] outside the skull. Thus the mandibular nerve [V3] is the only division of the trigeminal nerve that contains a motor component. +Outside the skull the motor fibers innervate the four muscles of mastication (temporalis, masseter, and medial and lateral pterygoids), as well as the tensor tympani muscle, the tensor veli palatini muscle, the anterior belly of the digastric muscle, and the mylohyoid muscle. +The mandibular nerve [V3] also receives sensory branches from the skin of the lower face, cheek, lower lip, anterior part of the external ear, part of the external acoustic meatus and the temporal region, the anterior two-thirds of the tongue, the teeth of the lower jaw, the mastoid air cells, the mucous membranes of the cheek, the + + + + +■ the ophthalmic nerve (ophthalmic division [V1]). ■ the maxillary nerve (maxillary division [V2]), and ■ the mandibular nerve (mandibular division [V3]). + +mandible, and dura in the middle cranial fossa. + + +Abducent nerve [VI] + + + +Ophthalmic nerve [V1] + +The ophthalmic nerve [V1] passes forward in the dura of the lateral wall of the cavernous sinus (see Fig. 8.45), leaves the cranial cavity, and enters the orbit through the superior orbital fissure (Fig. 8.53). +The ophthalmic nerve [V1] carries sensory branches from the eyes, conjunctiva, and orbital contents, including the lacrimal gland. It also receives sensory branches from the nasal cavity, frontal sinus, ethmoidal cells, falx cerebri, dura in the anterior cranial fossa and superior parts of the tentorium cerebelli, upper eyelid, dorsum of the nose, and the anterior part of the scalp. + +The abducent nerve [VI] carries GSE fibers to innervate the lateral rectus muscle in the orbit. It arises from the brainstem between the pons and medulla and passes forward, piercing the dura covering the clivus (Figs. 8.53 and 8.54). Continuing upward in a dural canal, it crosses the superior edge of the petrous part of the temporal bone, enters and crosses the cavernous sinus (see Fig. 8.45) just inferolateral to the internal carotid artery, and enters the orbit through the superior orbital fissure. + +Facial nerve [VII] +The facial nerve [VII] carries GSA, SA, GVE, and BE +fibers: 887 +Head and Neck + + + +■ The GSA fibers provide sensory input from part of the external acoustic meatus and deeper parts of the auricle. +■ The SA fibers are for taste from the anterior two-thirds of the tongue. +■ The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secre-tomotor activity in the lacrimal gland, submandibular and sublingual salivary glands, and glands in the mucous membranes of the nasal cavity, and hard and + +The chorda tympani carries taste (SA) fibers from the anterior two-thirds of the tongue and preganglionic para-sympathetic (GVE) fibers destined for the submandibular ganglion (Table 8.6). + + +Vestibulocochlear nerve [VIII] +The vestibulocochlear nerve [VIII] carries SA fibers for hearing and balance, and consists of two divisions: + +soft palates. +■ The BE fibers innervate the muscles of the face (muscles of facial expression) and scalp derived from the second pharyngeal arch, and the stapedius muscle, the posterior belly of the digastric muscle, and the stylohyoid muscle. + + +■ a vestibular component for balance, and ■ a cochlear component for hearing. + +The vestibulocochlear nerve [VIII] attaches to the lateral + + + + +The facial nerve [VII] attaches to the lateral surface of the brainstem, between the pons and medulla oblongata (Fig. 8.54). It consists of a large motor root and a smaller sensory root (the intermediate nerve): + +surface of the brainstem, between the pons and medulla, after emerging from the internal acoustic meatus and crossing the posterior cranial fossa (Figs. 8.53 and 8.54). The two divisions combine into the single nerve seen in the posterior cranial fossa within the substance of the petrous + + +■ The intermediate nerve contains the SA fibers for taste, the parasympathetic GVE fibers, and the GSA fibers. +■ The larger motor root contains the BE fibers. + +The motor and sensory roots cross the posterior cranial + +part of the temporal bone. + + +Glossopharyngeal nerve [IX] +The glossopharyngeal nerve [IX] carries GVA, GSA, SA, GVE, and BE fibers: + + + +fossa and leave the cranial cavity through the internal acoustic meatus (Fig. 8.53). After entering the facial canal in the petrous part of the temporal bone, the two roots fuse and form the facial nerve [VII]. Near this point the nerve enlarges as the geniculate ganglion, which is similar to a spinal ganglion containing cell bodies for sensory neurons. +At the geniculate ganglion the facial nerve [VII] turns and gives off the greater petrosal nerve, which carries mainly preganglionic parasympathetic (GVE) fibers (Table 8.6). +The facial nerve [VII] continues along the bony canal, giving off the nerve to the stapedius and the chorda tympani, before exiting the skull through the stylomastoid foramen. + + +■ The GVA fibers provide sensory input from the carotid body and sinus. +■ The GSA fibers provide sensory input from the posterior one-third of the tongue, palatine tonsils, oropharynx, and mucosa of the middle ear, pharyngotympanic tube, and mastoid air cells. +■ The SA fibers are for taste from the posterior one-third of the tongue. +■ The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secre-tomotor activity in the parotid salivary gland. +■ The BE fibers innervate the muscle derived from the third pharyngeal arch (the stylopharyngeus muscle). + + + + +Table 8.6 + + +Ganglion +Ciliary + +Parasympathetic ganglia of the head + +Cranial nerve origin of preganglionic fibers +Oculomotor nerve [III] + + + +Branch supplying preganglionic fibers to ganglion +Branch to ciliary ganglion + + + +Function +Innervation of sphincter pupillae muscle for pupillary constriction, and ciliary muscles for accommodation of the lens for near vision + + + +Pterygopalatine + +Otic +888 Submandibular + +Facial nerve [VII] + +Glossopharyngeal nerve [IX] +Facial nerve [VII] + +Greater petrosal nerve + +Lesser petrosal nerve +Chorda tympani to lingual + +Innervation of lacrimal gland, and mucous glands of nasal cavity, maxillary sinus, and palate +Innervation of parotid gland +Innervation of submandibular and sublingual glands +In the clinic + +Cranial nerve lesions + + +Cranial Nerve Olfactory nerve [I] Optic nerve [II] + +Oculomotor nerve [III] + + + + +Trochlear nerve [IV] + + +Trigeminal nerve [V] + + + + +Abducent nerve [VI] + + +Facial nerve [VII] + + + + + +Vestibulocochlear nerve [VIII] + +Glossopharyngeal nerve [IX] + +Vagus nerve [X] + + +Accessory nerve [XI] + + +Hypoglossal nerve [XII] + +Clinical Findings +Loss of smell (anosmia) + +Blindness/visual field abnormalities, loss of pupillary constriction + +Dilated pupil, ptosis, loss of normal pupillary reflex, eye moves down inferiorly and laterally (down and out) + + + +Inability to look inferiorly when the eye is adducted (down and in) + +Loss of sensation and pain in the region supplied by the three divisions of the nerve over the face; loss of motor function of the muscles of mastication on the side of the lesion + +Inability of lateral eye movement + + +Paralysis of facial muscles +Abnormal taste sensation from the anterior two-thirds of the tongue and dry conjunctivae Paralysis of contralateral facial muscles below the eye + +Progressive unilateral hearing loss and tinnitus (ringing in the ear) + +Loss of taste to the posterior one-third of the tongue and sensation of the soft palate + +Soft palate deviation with deviation of the uvula to the normal side; vocal cord paralysis + +Paralysis of sternocleidomastoid and trapezius muscles + +Atrophy of ipsilateral muscles of the tongue and deviation toward the affected side; speech disturbance + +Example of Lesion +Injury to the cribriform plate; congenital absence + +Direct trauma to the orbit; disruption of the optic pathway + +Pressure from an aneurysm arising from the posterior communicating, posterior cerebral, or superior cerebellar artery; pressure from a herniating cerebral uncus (false localizing sign); cavernous sinus mass or thrombosis + +Along the course of the nerve around the brainstem; orbital fracture + +Typically, in the region of the trigeminal ganglion, though local masses around the foramina through which the divisions pass can produce symptoms + + +Brain lesion or cavernous sinus lesion extending onto the orbit + +Damage to the branches within the parotid gland Injury to temporal bone; viral inflammation of nerve +Brainstem injury + + +Tumor at the cerebellopontine angle + + +Brainstem lesion; penetrating neck injury + + +Brainstem lesion; penetrating neck injury + + +Penetrating injury to the posterior triangle of the neck + +Penetrating injury to the neck and skull base pathology + + + + + +In the clinic + +Overview of cranial nerves + + +Corneal (blink) reflex + + + + +Cranial nerve reflexes +Pupillary (light) reflex + + + +■ Afferent—Trigeminal nerve (CN V) ■ Efferent—Facial nerve (CN VII) +Gag reflex +■ Afferent—Glossopharyngeal nerve (CN IX) ■ Efferent—Vagus nerve (CN X) + + +■ Afferent—optic nerve (CN II) +■ Efferent—oculomotor nerve (CN III) + + + +(continues) 889 +In the clinic—cont’d + + + +Olfactory nerve [I] + +Special sensory – smell + + +Optic nerve [II] + +Special sensory – vision + + + + + + + + +Oculomotor nerve [III] + +Somatic motor – five extra-ocular muscles (superior rectus, medial rectus, inferior oblique, inferior rectus, and levator palpebrae superioris) +Visceral motor – ciliary muscles and sphincter pupillae muscles + + + + + + +Trochlear nerve [IV] + +Somatic motor – one extra-ocular muscle (superior oblique) + +Abducent nerve [VI] + +Somatic motor – one extra-ocular muscle (lateral rectus) + + + + +V1 + + + +Trigeminal nerve [V] sensory root + +Somatic sensory – eyes, orbital contents, face, sinuses, teeth, nasal cavities, oral cavity, anterior 2/3 of tongue, nasopharynx, dura, anterior part of external ear,and part of external acoustic meatus + + +V2 + + +V3 + + + + + + +V3 +Trigeminal nerve [V] motor root + +Branchial motor – the four muscles of mastication +(medial pterygoid, lateral pterygoid, masseter, temporalis) and mylohyoid, anterior belly of digastric, tensor tympani, and tensor veli palatini + + + + +Efferent (motor) fibers + +Afferent (sensory) fibers + + +Fig. 8.55 Overview of cranial nerves. + +Facial nerve [VII] + +Branchial motor – all muscles of facial expression, and stapedius, stylohyoid, and posterior belly of digastric + + +Facial nerve [VII] (intermediate nerve) + +Special sensory – taste (anterior 2/3 of tongue) Somatic sensory – part of external acoustic meatus and deeper parts of auricle +Visceral motor (parasympathetic) – secretomotor to all salivary glands except for parotid gland; all mucous glands associated with the oral and nasal cavities; lacrimal gland + + + +Vestibulocochlear nerve [VIII] + +Special sensory – hearing and balance + + + + +Glossopharyngeal nerve [IX] + +Special sensory – taste (posterior 1/3 of tongue) Somatic sensory – posterior 1/3 of tongue, oropharynx, palatine tonsil, middle ear, pharyngotympanic tube, and mastoid air cells +Branchial motor – stylopharyngeus +Visceral motor – (parasympathetic) – secretomotor to the parotid gland +Visceral sensory – from carotid body and sinus + + + + + + + + + + + + + + + + + + + + + + + + +Hypoglossal nerve [XII] + +Somatic motor – all muscles of the tongue except palatoglossus + + + + + + + + +Accessory nerve [XI] + +Branchial motor – sternocleidomastoid and trapezius + +Vagus nerve [X] + +Somatic sensory – larynx, laryngopharynx, deeper parts of auricle, and part of external acoustic meatus +Special sensory – taste from epiglottis and pharynx Branchial motor – all muscles of pharynx except for stylopharyngeus; all muscles of the soft palate except for tensor veli palatini, all intrinsic muscles of larynx +Visceral motor – (parasympathetic) – thoracic viscera and abdominal viscera to end of midgut +Visceral sensory – thoracic viscera and abdominal viscera to end of midgut, chemo- and baroreceptors +(and in some cases carotid body) +Head and Neck + + + +The glossopharyngeal nerve [IX] arises as several rootlets on the anterolateral surface of the upper medulla oblongata (Fig. 8.54). The rootlets cross the posterior cranial fossa and enter the jugular foramen (Fig. 8.53). Within the jugular foramen, and before exiting from it, the rootlets merge to form the glossopharyngeal nerve. +Within or immediately outside the jugular foramen are two ganglia (the superior and inferior ganglia), which contain the cell bodies of the sensory neurons in the glos-sopharyngeal nerve [IX]. + +Tympanic nerve +Branching from the glossopharyngeal nerve [IX] either within or immediately outside the jugular foramen is the tympanic nerve. This branch reenters the temporal bone, enters the middle ear cavity, and participates in + +The vagus nerve arises as a group of rootlets on the anterolateral surface of the medulla oblongata just inferior to the rootlets arising to form the glossopharyngeal nerve [IX] (Fig. 8.54). The rootlets cross the posterior cranial fossa and enter the jugular foramen (Fig. 8.53). Within this foramen, and before exiting from it, the rootlets merge to form the vagus nerve [X]. Within or immedi-ately outside the jugular foramen are two ganglia, the superior (jugular) and inferior (nodose) ganglia, which contain the cell bodies of the sensory neurons in the vagus nerve [X]. + + +Accessory nerve [XI] +The accessory nerve [XI] is a cranial nerve that carries BE fibers to innervate the sternocleidomastoid and trapezius muscles (see Diogo R et al. Nature 2015;520:466–473). + +the formation of the tympanic plexus. Within the It is a unique cranial nerve because its roots arise from + +middle ear cavity it provides sensory innervation to the mucosa of the cavity, pharyngotympanic tube, and mastoid air cells. +The tympanic nerve also contributes GVE fibers, which leave the tympanic plexus in the lesser petrosal nerve—a small nerve that exits the temporal bone, enters the middle cranial fossa, and descends through the foramen ovale to exit the cranial cavity carrying preganglionic parasympa-thetic fibers to the otic ganglion (Table 8.6). + + +Vagus nerve [X] +The vagus nerve [X] carries GSA, GVA, SA, GVE, and BE fibers: + +motor neurons in the upper five segments of the cervical spinal cord. These fibers leave the lateral surface of the spinal cord and, joining together as they ascend, enter the cranial cavity through the foramen magnum (Fig. 8.54). The accessory nerve [XI] continues through the posterior cranial fossa and exits through the jugular foramen (Fig. 8.53). It then descends in the neck to innervate the ster-nocleidomastoid and trapezius muscles from their deep surfaces. + +Cranial root of the accessory nerve +Some descriptions of the accessory nerve [XI] refer to a few rootlets arising from the caudal part of the medulla oblongata on the anterolateral surface just inferior to the rootlets arising to form the vagus nerve [X] as the “cranial” + +■ The GSA fibers provide sensory input from the larynx, root of the accessory nerve (Fig. 8.54). Leaving the + +laryngopharynx, deeper parts of the auricle, part of the external acoustic meatus, and the dura mater in the posterior cranial fossa. +■ The GVA fibers provide sensory input from the aortic body chemoreceptors and aortic arch baroreceptors, and the esophagus, bronchi, lungs, heart, and abdomi-nal viscera in the foregut and midgut. +■ The SA fibers are for taste around the epiglottis and pharynx. +■ The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate smooth muscle and glands in the pharynx, larynx, thoracic + +medulla, the cranial roots course with the “spinal” roots of the accessory nerve [XI] into the jugular foramen, at which point the cranial roots join the vagus nerve [X]. As part of the vagus nerve [X], they are distributed to the pharyngeal musculature innervated by the vagus nerve [X] and are therefore described as being part of the vagus nerve [X]. + + +Hypoglossal nerve [XII] +The hypoglossal nerve [XII] carries GSE fibers to innervate all intrinsic muscles and most of the extrinsic muscles of + + + +viscera, and abdominal viscera of the foregut and midgut. + +the tongue. It arises as several rootlets from the anterior surface of the medulla (Fig. 8.54), passes laterally across + + + +■ The BE fibers innervate one muscle of the tongue (pala-toglossus), the muscles of the soft palate (except the tensor veli palatini), pharynx (except the stylopharyn- +892 geus), and larynx. + +the posterior cranial fossa, and exits through the hypoglos-sal canal (Fig. 8.53). This nerve innervates the hyoglossus, styloglossus, and genioglossus muscles and all intrinsic muscles of the tongue. +Regional Anatomy • Face 8 + + + +FACE + +A face-to-face meeting is an important initial contact between individuals. Part of this exchange is the use of facial expressions to convey emotions. In fact, a physician can gain important information about an individual’s general health by observing a patient’s face. +Thus an understanding of the unique organization + +arches superiorly, the lower edge of the mandible inferiorly, and as far back as the ears on either side, the area defined as the face, is particularly useful in the practice of medicine. + + +Muscles +The muscles of the face (Fig. 8.56) develop from the second + +of the various structures between the superciliary pharyngeal arch and are innervated by branches of the + + +Anterior auricular Superior auricular + + + + + +Frontal belly of occipitofrontalis + + + + + + +Orbicularis oculi + + +Procerus + +Nasalis + +Levator labii superioris alaeque nasi + + +Levator labii superioris + + +Zygomaticus minor + +Zygomaticus major + + + +Orbicularis oris + +Depressor labii inferioris + +Mentalis + +Depressor anguli oris + +Risorius + +Buccinator + +Platysma + + + +Fig. 8.56 Facial muscles. + + +Occipital belly of occipitofrontalis + + + + + + + +Posterior auricular + + + + + + + + +893 +Head and Neck + + + +facial nerve [VII]. They are in the superficial fascia, with origins from either bone or fascia, and insertions into the skin. +Because these muscles control expressions of the face, they are sometimes referred to as muscles of “facial expression.” They also act as sphincters and dilators of the orifices of the face (i.e., the orbits, nose, and mouth). This + +organizational arrangement into functional groups pro-vides a logical approach to understanding these muscles (Table 8.7). + +Orbital group +Two muscles are associated with the orbital group—the orbicularis oculi and the corrugator supercilii. + + + + + + + + + +Table 8.7 + +Muscle + +Muscles of the face + +Origin Insertion Innervation Function + + + +ORBITAL GROUP Orbicularis oculi —Palpebral part +—Orbital part + + +Corrugator supercilii + +NASAL GROUP Nasalis +—Transverse part + + +—Alar part + +Procerus + + +Depressor septi + +ORAL GROUP Depressor anguli oris + + +Depressor labii inferioris + +Mentalis + + + +Medial palpebral ligament +Nasal part of frontal bone; frontal process of maxilla; medial palpebral ligament +Medial end of the superciliary arch + + +Maxilla just lateral to nose + + +Maxilla over lateral incisor + +Nasal bone and upper part of lateral nasal cartilage + +Maxilla above medial incisor + + +Oblique line of mandible below canine, premolar, and first molar teeth +Anterior part of oblique line of mandible + +Mandible inferior to incisor teeth + + + +Lateral palpebral raphe +Fibers form an uninterrupted ellipse around orbit + +Skin of the medial half of eyebrow + + +Aponeurosis across dorsum of nose with muscle fibers from the other side +Alar cartilage of nose + +Skin of lower forehead between eyebrows + +Mobile part of the nasal septum + +Skin at the corner of mouth and blending with orbicularis oris +Lower lip at midline; blends with muscle from opposite side +Skin of chin + + + +Facial nerve [VII] Facial nerve [VII] + + +Facial nerve [VII] + + + +Facial nerve [VII] + + +Facial nerve [VII] + +Facial nerve [VII] + + +Facial nerve [VII] + + +Facial nerve [VII] + + +Facial nerve [VII] + + +Facial nerve [VII] + + + +Closes the eyelids gently Closes the eyelids forcefully + + +Draws the eyebrows medially and downward + + +Compresses nasal aperture + + +Draws cartilage downward and laterally, opening nostril +Draws down medial angle of eyebrows, producing transverse wrinkles over bridge of nose +Pulls nose inferiorly + + +Draws corner of mouth downward and laterally + +Draws lower lip downward and laterally + +Raises and protrudes lower lip as it wrinkles skin on chin + + + + + + + + + + + +894 +Regional Anatomy • Face 8 + + + +Table 8.7 + +Muscle +Risorius + +Muscles of the face—cont’d + +Origin +Fascia over masseter muscle + + + +Insertion +Skin at the corner of the mouth + + + +Innervation +Facial nerve [VII] + + + +Function +Retracts corner of mouth + + + +Zygomaticus major + +Zygomaticus minor + +Levator labii superioris + +Levator labii +superioris alaeque nasi +Levator anguli oris + +Orbicularis oris + +Buccinator + + +OTHER MUSCLES OR GROUPS +Anterior auricular + +Superior auricular + +Posterior auricular + +Occipitofrontalis —Frontal belly + +—Occipital belly + +Posterior part of lateral surface of zygomatic bone +Anterior part of lateral surface of zygomatic bone +Infra-orbital margin of maxilla + +Frontal process of maxilla + +Maxilla below infra-orbital foramen +From muscles in area; maxilla and mandible in midline +Posterior parts of maxilla and mandible; pterygomandibular raphe + + +Anterior part of temporal fascia +Epicranial aponeurosis on side of head +Mastoid process of temporal bone + +Skin of eyebrows + +Lateral part of superior nuchal line of occipital bone and mastoid process of temporal bone + +Skin at the corner of the mouth +Upper lip just medial to corner of mouth +Skin of upper lateral half of upper lip +Alar cartilage of nose and upper lip +Skin at the corner of mouth + +Forms ellipse around mouth + +Blends with orbicularis oris and into lips + + + +Into helix of ear + +Upper part of auricle + +Convexity of concha of ear + + +Into galea aponeurotica + +Into galea aponeurotica + +Facial nerve [VII] + +Facial nerve [VII] + +Facial nerve [VII] + +Facial nerve [VII] + +Facial nerve [VII] + +Facial nerve [VII] + +Facial nerve [VII] + + + + +Facial nerve [VII] + +Facial nerve [VII] + +Facial nerve [VII] + + +Facial nerve [VII] + +Facial nerve [VII] + +Draws the corner of the mouth upward and laterally +Draws the upper lip upward + +Raises upper lip; helps form nasolabial furrow +Raises upper lip and opens nostril +Raises corner of mouth; helps form nasolabial furrow +Closes lips; protrudes lips + +Presses the cheek against teeth; compresses distended cheeks + + + +Draws ear upward and forward + +Elevates ear + +Draws ear upward and backward + + +Wrinkles forehead; raises eyebrows +Draws scalp backward + + + + + +Orbicularis oculi +The orbicularis oculi is a large muscle that completely surrounds each orbital orifice and extends into each eyelid (Fig. 8.57). It closes the eyelids. It has two major parts: + + +An additional small lacrimal part of the orbicularis oculi muscle is deep, medial in position, and attaches to bone posterior to the lacrimal sac of the lacrimal apparatus in the orbit. + + + +■ The outer orbital part is a broad ring that encircles the orbital orifice and extends outward beyond the orbital rim. +■ The inner palpebral part is in the eyelids and consists of muscle fibers originating in the medial corner of the eye that arch across each lid to attach laterally. + +The orbital and palpebral parts have specific roles to + +Corrugator supercilii +The second muscle in the orbital group is the much smaller corrugator supercilii (Fig. 8.57), which is deep to the eyebrows and the orbicularis oculi muscle and is active when frowning. It arises from the medial end of the super-ciliary arch, passing upward and laterally to insert into the skin of the medial half of the eyebrow. It draws the eye-brows toward the midline, causing vertical wrinkles above + +play during eyelid closure. The palpebral part closes the eye the nose. gently, whereas the orbital part closes the eye more force- +fully and produces some wrinkling on the forehead. +895 +Head and Neck + + +Corrugator supercilii + + + + + +Orbital Orbicularis oculi Palpebral + + + + + + + + + + +Fig. 8.57 Orbital group of facial muscles. + + + +Nasal group +Three muscles are associated with the nasal group—the nasalis, the procerus, and the depressor septi nasi (Fig. 8.58). + +Nasalis +The largest and best developed of the muscles of the nasal +group is the nasalis, which is active when the nares are Procerus +flared (Fig. 8.58). It consists of a transverse part (the compressor naris) and an alar part (the dilator naris): + + +■ The transverse part of the nasalis compresses the nares—it originates from the maxilla and its fibers pass upward and medially to insert, along with fibers from the same muscle on the opposite side, into an aponeu-rosis across the dorsum of the nose. +■ The alar part of the nasalis draws the alar cartilages downward and laterally, so opening the nares—it origi-nates from the maxilla, below and medial to the trans-verse part, and inserts into the alar cartilage. + + +Transverse part +Nasalis + +Alar part + + + +Procerus +The procerus is a small muscle superficial to the nasal bone and is active when an individual frowns (Fig. 8.58). + + +Depressor septi nasi + +Fig. 8.58 Nasal group of facial muscles. + + + + + + + + +896 +Regional Anatomy • Face 8 + + + +It arises from the nasal bone and the upper part of the lateral nasal cartilage and inserts into the skin over the lower part of the forehead between the eyebrows. It may be continuous with the frontal belly of the occipitofrontalis muscle of the scalp. +The procerus draws the medial border of the eyebrows downward to produce transverse wrinkles over the bridge of the nose. + +Depressor septi nasi +The final muscle in the nasal group is the depressor septi nasi, another muscle that assists in widening the nares (Fig. 8.58). Its fibers arise from the maxilla above the central incisor tooth and ascend to insert into the lower part of the nasal septum. +The depressor septi nasi pulls the nose inferiorly, so assisting the alar part of the nasalis in opening the nares. + +Levator labii superioris alaeque nasi +Levator labii superioris + + +Oral group +The muscles in the oral group move the lips and cheek. They include the orbicularis oris and buccinator muscles, and a lower and upper group of muscles (Fig. 8.59). Many of these muscles intersect just lateral to the corner of the mouth on each side at a structure termed the modiolus. + +Orbicularis oris +The orbicularis oris is a complex muscle consisting of fibers that completely encircle the mouth (Fig. 8.59). Its function is apparent when pursing the lips, as occurs during whistling. Some of its fibers originate near the midline from the maxilla superiorly and the mandible inferiorly, whereas other fibers are derived from both the buccinator, in the cheek, and the numerous other muscles + +Levator anguli oris + + + + + +Zygomaticus minor + + +Zygomaticus major Buccinator + +Modiolus + +Risorius + +Platysma + + + + +Depressor anguli oris + +Depressor labii inferioris + + + +Orbicularis oris + +Mentalis + + +Fig. 8.59 Oral group of facial muscles. + + +In the clinic + +Facelifts and botox +Facelift surgery (rhytidectomy) aims to lift up and pull back the skin in the lower half of the face and neck to make the face more taught. Careful placement of the incisions is important to ensure there is no skin or facial distortion and to avoid hair loss. The commonest incisions are placed in the temporal region on each side, extending to the helices of the ears, then tracking behind the tragus, around the earlobes, and then to the occiput. + + + +Botox is derived from the toxin produced by the bacterium Clostridium botulinum, which blocks neuromuscular junctions resulting in muscle relaxation. It is used in many therapies including strabismus (crossed eyes) where it is injected into extra-ocular muscles. Its injection is also used to treat uncontrolled blinking (blepharospasm), spastic muscle conditions, and overactive bladder disorders, as well as to relax facial muscles to improve the cosmetic appearances of lines and wrinkles and to treat patients with +excessive sweating (hyperhidrosis). 897 +Head and Neck + + + +acting on the lips. It inserts into the skin and mucous membrane of the lips, and into itself. +Contraction of the orbicularis oris narrows the mouth and closes the lips. + +Buccinator +The buccinator forms the muscular component of the cheek and is used every time air expanding the cheeks is forcefully expelled (Figs. 8.59 and 8.60). It is in the space between the mandible and the maxilla, deep to the other facial muscles in the area. +The buccinator arises from the posterior part of the maxilla and mandible opposite the molar teeth and the pterygomandibular raphe, which is a tendinous band between the pterygoid hamulus superiorly and the man- + +The fibers of the buccinator pass toward the corner of the mouth to insert into the lips, blending with fibers from the orbicularis oris in a unique fashion. Central fibers of the buccinator cross so that lower fibers enter the upper lip and upper fibers enter the lower lip (Fig. 8.60). The highest and lowest fibers of the buccinator do not cross and enter the upper and lower lips, respectively. +Contraction of the buccinator presses the cheek against the teeth. This keeps the cheek taut and aids in mastication by preventing food from accumulating between the teeth and the cheek. The muscle also assists in the forceful expul-sion of air from the cheeks. + +Lower group of oral muscles +The muscles in the lower group consist of the depressor + +dible inferiorly and is a point of attachment for the bucci- anguli oris, depressor labii inferioris. and mentalis nator and superior pharyngeal constrictor muscles. (Fig. 8.59). + + + + + + +Parotid duct (cut) + +■ The depressor anguli oris is active during frowning. It arises along the side of the mandible below the canine, premolar, and first molar teeth and inserts into skin and the upper part of the orbicularis oris near the corner of the mouth. It depresses the corner of the mouth. +■ The depressor labii inferioris arises from the front of the mandible, deep to the depressor anguli oris. Its fibers move superiorly and medially, some merging with fibers from the same muscle on the opposite side and fibers from the orbicularis oris before inserting into the lower lip. It depresses the lower lip and moves it laterally. +■ The mentalis helps position the lip when drinking from a cup or when pouting. It is the deepest muscle of the lower group arising from the mandible just inferior to the incisor teeth, with its fibers passing downward and medially to insert into the skin of the chin. It raises and protrudes the lower lip as it wrinkles the skin of the chin. + + +Upper group of oral muscles +The muscles of the upper group of oral muscles consist of the risorius, zygomaticus major, zygomaticus minor, levator labii superioris, levator labii superioris alaeque nasi, and +Buccinator muscle levator anguli oris (Fig. 8.59). + + +Pterygomandibular raphe + +Superior pharyngeal constrictor muscle + + +898 Fig. 8.60 Buccinator muscle. + +■ The risorius helps produce a grin (Fig. 8.59). It is a thin, superficial muscle that extends laterally from the corner of the mouth in a slightly upward direction. Contraction of its fibers pulls the corner of the mouth laterally and upward. +■ The zygomaticus major and zygomaticus minor help produce a smile (Fig. 8.59). The zygomaticus major +Regional Anatomy • Face 8 + + + +is a superficial muscle that arises deep to the orbicularis oculi along the posterior part of the lateral surface of the zygomatic bone, and passes downward and forward, blending with the orbicularis oris and inserting into skin at the corner of the mouth. The zygomaticus minor arises from the zygomatic bone anterior to the origin of the zygomaticus major, parallels the path of the zygo-maticus major, and inserts into the upper lip medial to the corner of the mouth. Both zygomaticus muscles raise the corner of the mouth and move it laterally. +■ The levator labii superioris deepens the furrow between the nose and the corner of the mouth during sadness (Fig. 8.59). It arises from the maxilla just supe-rior to the infra-orbital foramen, and its fibers pass downward and medially to blend with the orbicularis oris and insert into the skin of the upper lip. +■ The levator labii superioris alaeque nasi is medial to the levator labii superioris, arises from the maxilla next to the nose, and inserts into both the alar cartilage of the nose and skin of the upper lip (Fig. 8.59). It may assist in flaring the nares. +■ The levator anguli oris is more deeply placed and covered by the other two levators and the zygomaticus muscles (Fig. 8.59). It arises from the maxilla, just inferior to the infra-orbital foramen and inserts into the skin at the corner of the mouth. It elevates the corner of the mouth and may help deepen the furrow between the nose and the corner of the mouth during sadness. + + +Superior auricular + + + + + + + + + + + + + + + + + + + + + + + + + + +Anterior auricular + +Posterior auricular + +Fig. 8.61 Auricular muscles. + + + +Other muscles or muscle groups +Several additional muscles or groups of muscles not in the area defined as the face, but derived from the second pharyngeal arch and innervated by the facial nerve [VII], are considered muscles of facial expression. They include the platysma, auricular, and occipitofrontalis muscles (see Fig. 8.56). + + + +■ The anterior muscle is anterolateral and pulls the ear upward and forward. +■ The superior muscle is superior and elevates the ear. +■ The posterior muscle is posterior and retracts and ele-vates the ear. + + + +Platysma +The platysma is a large, thin sheet of muscle in the super-ficial fascia of the neck. It arises below the clavicle in the upper part of the thorax and ascends through the neck to the mandible. At this point, the more medial fibers insert on the mandible, whereas the lateral fibers join with + +Occipitofrontalis +The occipitofrontalis is the final muscle in this category of “other muscles of facial expression” and is associated with the scalp (see Fig. 8.56). It consists of a frontal belly anteriorly and an occipital belly posteriorly. An aponeurotic tendon connects the two: + + + +muscles around the mouth. +The platysma tenses the skin of the neck and can move the lower lip and corners of the mouth down. + +Auricular muscles +Three of these muscles, “other muscles of facial expres- + + +■ The frontal belly covers the forehead and is attached to the skin of the eyebrows. +■ The occipital belly arises from the posterior aspect of the skull and is smaller than the frontal belly. + + + +sion,” are associated with the ear—the anterior, superior, and posterior auricular muscles (Fig. 8.61): + +The occipitofrontalis muscles move the scalp and wrinkle the forehead. 899 +Head and Neck + + + + +Parotid gland +The parotid glands are the largest of the three pairs of main salivary glands in the head and numerous structures pass through them. They are anterior to and below the lower half of the ear, superficial, posterior, and deep to the ramus of the mandible (Fig. 8.62). They extend down to the lower border of the mandible and up to the zygomatic + +sternocleidomastoid muscle and continue anteriorly to halfway across the masseter muscle. +The parotid duct leaves the anterior edge of the parotid gland midway between the zygomatic arch and the corner of the mouth (Fig. 8.62). It crosses the face in a transverse direction and, after crossing the medial border of the mas-seter muscle, turns deeply into the buccal fat pad and pierces the buccinator muscle. It opens into the oral cavity + +arch. Posteriorly they cover the anterior part of the near the second upper molar tooth. + + +Maxillary artery and vein + +Transverse facial artery and vein Superficial temporal artery and vein + + + + + + + +Temporal branches + + + + + +Zygomatic branches + +Facial nerve [VII] + + + +Parotid duct + +Buccal branches + + +Buccinator + +Masseter + +Marginal mandibular branches + +Posterior auricular artery + +Retromandibular vein + + +Parotid gland + +External carotid artery + +External jugular vein + + +A Cervical branches + + + +Medial pterygoid muscle + +Mandible + + + + +Masseter muscle + +Retromandibular vein External carotid artery + +Styloid process + + + + +Mastoid process + + +B Parotid gland Facial nerve [VII] + +900 Fig. 8.62 Parotid gland. A. Lateral view. B. Cross section. +Regional Anatomy • Face 8 + + + + +Important relationships +Several major structures enter and pass through or pass just deep to the parotid gland. These include the facial nerve [VII], the external carotid artery and its branches, and the retromandibular vein and its tributaries + +■ The maxillary artery passes horizontally, deep to the mandible. +■ The superficial temporal artery continues in a superior direction and emerges from the upper border of the gland after giving off the transverse facial artery. + + + +(Fig. 8.62). + +Facial nerve +The facial nerve [VII] exits the skull through the stylomas-toid foramen and then passes into the parotid gland, where it usually divides into upper and lower trunks. These pass through the substance of the parotid gland, where there may be further branching and anastomosing of the nerves. Five terminal groups of branches of the facial nerve [VII]—the temporal, zygomatic, buccal, marginal + + +Retromandibular vein and its tributaries +The retromandibular vein is formed in the substance of the parotid gland when the superficial temporal and maxil-lary veins join together (Fig. 8.62), and passes inferiorly in the substance of the parotid gland. It usually divides into anterior and posterior branches just below the inferior border of the gland. + +Arterial supply + +mandibular, and cervical branches—emerge from The parotid gland receives its arterial supply from the + +the upper, anterior, and lower borders of the parotid gland (Fig. 8.62). +The intimate relationships between the facial nerve [VII] and the parotid gland mean that surgical removal of the parotid gland is a difficult dissection if all branches of the facial nerve [VII] are to be spared. + +External carotid artery and its branches +The external carotid artery enters into or passes deep to the inferior border of the parotid gland (Fig. 8.62). As it con-tinues in a superior direction, it gives off the posterior auricular artery before dividing into its two terminal + +numerous arteries that pass through its substance. + +Innervation +Sensory innervation of the parotid gland is provided by the auriculotemporal nerve, which is a branch of the man-dibular nerve [V3]. This division of the trigeminal nerve exits the skull through the foramen ovale. +The auriculotemporal nerve also carries secretomotor fibers to the parotid gland. These postganglionic parasym-pathetic fibers have their origin in the otic ganglion associ-ated with the mandibular nerve [V3] and are just inferior to the foramen ovale. Preganglionic parasympathetic fibers + + + +branches (the maxillary and superficial temporal arteries) near the lower border of the ear: + +to the otic ganglion come from the glossopharyngeal nerve [IX]. + + + + + + + + + + + + + + + + + + + + + + + +901 +Head and Neck + + + +In the clinic + +Parotid gland +The parotid gland is the largest of the paired salivary glands and is enclosed within the split investing layer of deep cervical fascia. +The parotid gland produces a watery saliva and salivary amylase, which are necessary for food bolus formation, oral digestion, and smooth passage of the bolus into the upper gastrointestinal tract. +Tumors of the parotid gland +The commonest tumors of the parotid gland (Fig. 8.63) are benign and typically involve the more superficial part of the gland. These include pleomorphic adenoma and adenolymphoma. Their importance is in relation to their anatomical position. The relationship of any tumor to the branches of the facial nerve [VII] must be defined because resection of the tumor may damage the nerve. + + + +Parotid gland Right internal Maxilla carotid artery + + + +Body of mandible + + + +Parotid gland stones +It is not uncommon for stones to develop within the parotid gland. They typically occur within the main confluence of the ducts and within the main parotid duct. The patient usually complains of intense pain when salivating and tends to avoid foods that produce this symptom. The pain can be easily reproduced in the clinic by squirting lemon juice into the patient’s mouth. +Surgery depends upon where the stone is. If it is within the anterior aspect of the duct, a simple incision in the buccal mucosa with a sphincterotomy may allow removal. If the stone is farther back within the main duct, complete gland excision may be necessary. + + + + + + + + + + + +Styloid process Right jugular vein Tumor in left parotid gland + +Fig. 8.63 Tumor in parotid gland. Axial CT scan. + + + + + + + + + + + + + + + + + + + + + + + +902 +Regional Anatomy • Face 8 + + +Innervation +During development a cranial nerve becomes associated with each of the pharyngeal arches. Because the face is primar-ily derived from the first and second pharyngeal arches, innervation of neighboring facial structures is as follows: + + +[V3]—before leaving the middle cranial fossa (Fig. 8.64). Each of these divisions passes out of the cranial cavity to innervate a part of the face, so most of the skin covering the face is innervated solely by branches of the trigeminal nerve [V]. The exception is a small area covering the angle + + + + +■ The trigeminal nerve [V] innervates facial structures derived from the first arch. +■ The facial nerve [VII] innervates facial structures + +and lower border of the ramus of the mandible and parts of the ear, where the facial [VII], vagus [X], and cervical nerves contribute to the innervation. + + + +derived from the second arch. + +Sensory innervation +Because the face is derived developmentally from a number of structures originating from the first pharyngeal arch, cutaneous innervation of the face is by branches of the + + +Ophthalmic nerve [V1] +The ophthalmic nerve [V1] exits the skull through the superior orbital fissure and enters the orbit. Its branches (Fig. 8.64) that innervate the face include: + + + +trigeminal nerve [V]. +The trigeminal nerve [V] divides into three major divisions— the ophthalmic [V1], maxillary [V2], and mandibular + +■ the supra-orbital and supratrochlear nerves, which leave the orbit superiorly and innervate the upper eyelid, forehead, and scalp; + + +Ophthalmic nerve [V1] +Maxillary nerve [V2] Zygomaticotemporal +nerve + + + +Supra-orbital nerve + +Supratrochlear nerve + + +Lacrimal nerve + +Infratrochlear nerve + + + +Auriculotemporal nerve + + +External nasal nerve + +Infra-orbital nerve +Superior orbital fissure + + +Mandibular +nerve [V3] +Orbit + + +Trigeminal ganglion + +V1 V + + + + +Mental nerve + + + +Buccal nerve + +Foramen rotundum + + +Zygomaticofacial nerve + + +Pteryrgopalatine fossa + + +V2 V3 +Foramen ovale + + +Infratemporal fossa + + + + +Fig. 8.64 Trigeminal nerve [V] leaving the skull. 903 +Head and Neck + + + +■ the infratrochlear nerve, which exits the orbit in the medial angle to innervate the medial half of the upper eyelid, the skin in the area of the medial angle, and the side of the nose; +■ the lacrimal nerve, which exits the orbit in the lateral angle to innervate the lateral half of the upper eyelid and the skin in the area of the lateral angle; and +■ the external nasal nerve, which supplies the anterior part of the nose (Fig. 8.65). + +■ a small zygomaticotemporal branch, which exits the zygomatic bone and supplies a small area of the anterior temple above the zygomatic arch; +■ a small zygomaticofacial branch, which exits the zygomatic bone and supplies a small area of skin over the zygomatic bone; and +■ the large infra-orbital nerve, which exits the maxilla through the infra-orbital foramen and immediately divides into multiple branches to supply the lower eyelid, cheek, side of the nose, and upper lip (Fig. 8.65). + + +Maxillary nerve [V2] +The maxillary nerve [V2] exits the skull through the foramen rotundum. Branches (Fig. 8.64) that innervate the face include: + + + + +Ophthalmic nerve [V1] + + + + + +Zygomaticotemporal nerves + +Supratrochlear nerve + +Supra-orbital nerve + + +Infratrochlear nerve + +Maxillary nerve [V2] + +External nasal nerve + + +Infra-orbital nerve + +Zygomaticofacial nerve + + + + +Mental nerve + +Greater occipital (from posterior ramus of C2) + + + + + +Auriculotemporal nerve + + + + + + +Third occipital +(from posterior ramus of C3) + +Lesser occipital nerve +Lesser occipital and great auricular (from cervical plexus) +Great auricular nerve (from anterior ramus of C2 and C3) + + + +Buccal nerve + +Mandibular nerve [V3] + + +Transverse cervical +(from anterior ramus of C2 and C3) + + +Transverse cervical + + +904 Fig. 8.65 Cutaneous distribution of the trigeminal nerve [V]. +Regional Anatomy • Face 8 + + + + +Mandibular nerve [V3] +The mandibular nerve [V3] exits the skull through the foramen ovale. Branches (Fig. 8.65) innervating the face include: + +Once in the parotid gland, the main stem of the facial nerve [VII] usually divides into upper (temporofacial) and lower (cervicofacial) branches. As these branches pass through the substance of the parotid gland they may branch further or take part in an anastomotic network (the + + + + +■ the auriculotemporal nerve, which enters the face just posterior to the temporomandibular joint, passes through the parotid gland, and ascends just anterior to the ear to supply the external acoustic meatus, the surface of the tympanic membrane (eardrum), and a large area of the temple; +■ the buccal nerve, which is on the surface of the buc-cinator muscle supplying the cheek; and + +parotid plexus). +Whatever types of interconnections occur, five terminal groups of branches of the facial nerve [VII]—the temporal, zygomatic, buccal, marginal mandibular, and cervical branches—emerge from the parotid gland (Fig. 8.66A). +Although there are variations in the pattern of distribu-tion of the five terminal groups of branches, the basic pattern is as follows: + + + +■ the mental nerve, which exits the mandible through the mental foramen and immediately divides into mul-tiple branches to supply the skin and mucous membrane of the lower lip and skin of the chin (Fig. 8.65). + +■ Temporal branches exit from the superior border of the parotid gland to supply muscles in the area of the temple, forehead, and supra-orbital area. +■ Zygomatic branches emerge from the anterosuperior border of the parotid gland to supply muscles in the + + + + +Motor innervation +The muscles of the face, as well as those associated with the external ear and the scalp, are derived from the second pharyngeal arch. The cranial nerve associated with this arch is the facial nerve [VII] and therefore branches of the facial nerve [VII] innervate all these muscles. +The facial nerve [VII] exits the posterior cranial fossa through the internal acoustic meatus. It passes through the temporal bone, giving off several branches, and emerges + +infra-orbital area, the lateral nasal area, and the upper lip. +■ Buccal branches emerge from the anterior border of the parotid gland to supply muscles in the cheek, the upper lip, and the corner of the mouth. +■ Marginal mandibular branches emerge from the anteroinferior border of the parotid gland to supply muscles of the lower lip and chin. +■ Cervical branches emerge from the inferior border of the parotid gland to supply the platysma. + + + +from the base of the skull through the stylomastoid foramen (Fig. 8.66). At this point it gives off the posterior auricu-lar nerve. This branch passes upward, behind the ear, to supply the occipital belly of the occipitofrontalis muscle of the scalp and the posterior auricular muscle of the ear. +The main stem of the facial nerve [VII] then gives off another branch, which innervates the posterior belly of the digastric muscle and the stylohyoid muscle. At this point, the facial nerve [VII] enters the deep surface of the parotid gland (Fig. 8.66B). + + +Vessels + +The arterial supply to the face is primarily from branches of the external carotid artery, though there is some limited supply from a branch of the internal carotid artery. +Similarly, most of the venous return is back to the internal jugular vein, though some important connections from the face result in venous return through a clinically relevant intracranial pathway involving the cavernous sinus. + + + + + + + + + + + + + + +905 +Head and Neck + + + + + + + +Temporal branches + + +Temporofacial branch + + +Zygomatic branches + +Posterior auricular nerve + + + +Buccal branches Cervicofacial branch + + +Parotid gland + + + + +Marginal mandibular branches + + +A Cervical branches + + + +Facial nerve [VII] + +Temporofacial branch + + + +Cervicofacial branch + + +B + +External acoustic meatus + +Posterior auricular nerve + +Mastoid process + +Digastric branch + +Digastric muscle + +Mandible + + +Fig. 8.66 Facial nerve [VII] on the face. A. Terminal branches. B. Branches before entering the parotid gland. + + + + + +Arteries Facial artery +The facial artery is the major vessel supplying the face (Fig. 8.67). It branches from the anterior surface of the external carotid artery, passes up through the deep struc-tures of the neck, and appears at the lower border of the mandible after passing posterior to the submandibular + + +artery runs upward and medially in a tortuous course. It passes along the side of the nose and terminates as the angular artery at the medial corner of the eye. +Along its path the facial artery is deep to the platysma, risorius, and zygomaticus major and minor, superficial to the buccinator and levator anguli oris, and may pass superficially to or through the levator labii superioris. + +gland. Curving around the inferior border of the mandible Branches of the facial artery include the superior + +just anterior to the masseter, where its pulse can be felt, the 906 facial artery then enters the face. From this point the facial + +and inferior labial branches and the lateral nasal branch (Fig. 8.67). +Regional Anatomy • Face 8 + + + +Zygomaticofacial artery and vein + +Zygomaticotemporal artery and vein + +Transverse facial artery and vein + +Superficial temporal artery and vein + + + + + +Supratrochlear artery and vein + + +Supra-orbital artery and vein + + +Angular artery and vein Dorsal nasal artery and vein +Lateral nasal artery and vein +Posterior auricular vein + + +Superior labial artery and vein + +Posterior auricular artery + +Occipital vein + + +Occipital artery + + +External jugular vein +Inferior labial artery and vein + +Facial artery +A Facial vein + +External carotid artery Internal jugular vein + + +Transverse facial artery + + +Superficial temporal artery + +Maxillary artery +Infra-orbital artery + +Buccal artery + +External carotid artery + +Lingual artery + +Mental artery +Facial artery + +B + +Fig. 8.67 Vasculature of the face. A. Lateral view. B. Branches of the maxillary artery. + + +907 +Head and Neck + + +The labial branches arise near the corner of the mouth: ■ The mental artery enters the face through the mental + + +■ The inferior labial branch supplies the lower lip. +■ The superior labial branch supplies the upper lip, and also provides a branch to the nasal septum. + +Near the midline, the superior and inferior labial + +foramen and supplies the chin. + +Branches of the ophthalmic artery +Three small arteries from the internal carotid artery also contribute to the arterial supply of the face. These vessels arise from the ophthalmic artery, a branch of the inter- + + + +branches anastomose with their companion arteries from the opposite side of the face. This provides an important + +nal carotid artery, after the ophthalmic artery enters the orbit: + + + +connection between the facial arteries and the external carotid arteries of opposite sides. +The lateral nasal branch is a small branch arising from the facial artery as it passes along the side of the nose. It supplies the lateral surface and dorsum of the nose. + +Transverse facial artery +Another contributor to the vascular supply of the face is the transverse facial artery (Fig. 8.67), which is a branch of the superficial temporal artery (the smaller of the two terminal branches of the external carotid artery). +The transverse facial artery arises from the superficial + + +■ The zygomaticofacial and zygomaticotemporal arteries come from the lacrimal branch of the ophthal-mic artery (Fig. 8.67), enter the face through the zygomaticofacial and zygomaticotemporal foramina, and supply the area of the face over the zygomatic bone. +■ The dorsal nasal artery, a terminal branch of the ophthalmic artery, exits the orbit in the medial corner, and supplies the dorsum of the nose. +■ The supraorbital and supratrochlear arteries supply the anterior scalp. + + + +temporal artery within the substance of the parotid gland, passes through the gland, and crosses the face in a trans-verse direction. Lying on the superficial surface of the masseter muscle, it is between the zygomatic arch and the parotid duct. + +Branches of the maxillary artery + + +Veins Facial vein +The facial vein is the major vein draining the face (Fig. 8.67). Its point of origin is near the medial corner of the orbit as the supratrochlear and supra-orbital veins come together to form the angular vein. This vein becomes + +The maxillary artery, the larger of the two terminal the facial vein as it proceeds inferiorly and assumes a posi- + +branches of the external carotid artery, gives off several small branches which contribute to the arterial supply to the face: + +tion just posterior to the facial artery. The facial vein descends across the face with the facial artery until it reaches the inferior border of the mandible. Here the artery and vein part company and the facial vein passes superficial + + + +■ The infra-orbital artery enters the face through the infra-orbital foramen and supplies the lower eyelid, upper lip, and the area between these structures. +■ The buccal artery enters the face on the superficial surface of the buccinator muscle and supplies structures in this area. + +to the submandibular gland to enter the internal jugular vein. +Throughout its course the facial vein receives tributar-ies from veins draining the eyelids, external nose, lips, cheek, and chin that accompany the various branches of the facial artery. + + + + + + + + + + + + + + +908 +Regional Anatomy • Face 8 + + + + +Transverse facial vein +The transverse facial vein is a small vein that accompanies the transverse facial artery in its journey across the face (Fig. 8.67). It empties into the superficial temporal vein within the substance of the parotid gland. + +Intracranial venous connections +As it crosses the face, the facial vein has numerous connec-tions with venous channels passing into deeper regions of the head (Fig. 8.68): + +channels in the head, so blood can move in any direction. Because of the interconnections between the veins, infec-tions of the face, primarily above the mouth (i.e., the “danger area”) should be handled with great care to prevent the dissemination of infectious material in an intracranial direction. + +Lymphatic drainage +Lymphatic drainage from the face primarily moves toward three groups of lymph nodes (Fig. 8.69): + + + + +■ near the medial corner of the orbit, it communicates with ophthalmic veins; +■ in the area of the cheek it communicates with veins passing into the infra-orbital foramen; +■ it also communicates with veins passing into deeper regions of the face (i.e., the deep facial vein connecting with the pterygoid plexus of veins). + +All these venous channels have interconnections with + +■ submental nodes inferior and posterior to the chin, which drain lymphatics from the medial part of the lower lip and chin bilaterally; +■ submandibular nodes superficial to the submandibu-lar gland and inferior to the body of the mandible, which drain the lymphatics from the medial corner of the orbit, most of the external nose the medial part of the cheek, the upper lip, and the lateral part of the lower lip that follows the course of the facial artery; +■ pre-auricular and parotid nodes anterior to the + + + +the intracranial cavernous sinus through emissary veins that connect intracranial with extracranial veins. There are no valves in the facial vein or any other venous + +ear, which drain lymphatics from most of the eyelids, a part of the external nose, and the lateral part of the cheek. + + + + + + + +Ophthalmic veins + + + + + + + + + + + + + + + + + + + +Infra-orbital vein Facial vein +Deep facial vein + +Cavernous sinus + + + + + + + + + + + + + + + + + + + + +Pterygoid plexus of veins + + + + + + + + + + + + + + + + + + + +Submental nodes + +Submandibular nodes + +Pre-auricular and parotid nodes + + +Fig. 8.68 Intracranial venous connections. Fig. 8.69 Lymphatic drainage of the face. 909 +Head and Neck + + + +In the clinic + +Facial nerve [VII] palsy (Bell’s palsy) +The complexity of the facial nerve [VII] is demonstrated by the different pathological processes and sites at which these processes occur. +The facial nerve [VII] is formed from the nuclei within the brainstem emerging at the junction of the pons and the +medulla. It enters the internal acoustic meatus, passes to the geniculate ganglion (which gives rise to further branches), and emerges from the skull base after a complex course within the temporal bone, leaving through the stylomastoid foramen. It enters the parotid gland and gives rise to five terminal groups of branches that supply muscles in the face and a number of additional branches that supply deeper or more posterior muscles. A series of lesions may affect the nerve along its course, and it is possible, with good clinical expertise, to determine the exact site of the lesion in relation to the course of the nerve. +Central lesions +A primary brainstem lesion affecting the motor nucleus of the facial nerve [VII] would lead to ipsilateral (same side) weakness of the whole face. However, because the upper part of the nucleus receives motor input from the left and right cerebral hemispheres a lesion occurring above the nucleus leads to contralateral lower facial weakness. In this + + + + + + + + +In the clinic + +Trigeminal neuralgia +Trigeminal neuralgia (tic douloureux) is a complex sensory disorder of the sensory root of the trigeminal nerve. Typically the pain is in the region of the mandibular [V3] and maxillary [V2] nerves, and is usually of sudden onset, is excruciating in nature, and may be triggered by touching a sensitive region of skin. +The etiology of trigeminal neuralgia is unknown, although anomalous blood vessels lying adjacent to the + + + +example, motor innervation to the upper face is spared because the upper part of the nucleus receives input from both hemispheres. Preservation and loss of the special functions are determined by the extent of the lesion. +Lesions at and around the geniculate ganglion +Typically lesions at and around the geniculate ganglion are accompanied by loss of motor function on the whole of the ipsilateral (same) side of the face. Taste to the anterior +two-thirds of the tongue, lacrimation, and some salivation also are likely to be affected because the lesion is proximal to the greater petrosal and chorda tympani branches of the nerve. +Lesions at and around the stylomastoid foramen Lesions at and around the stylomastoid foramen are the commonest abnormality of the facial nerve [VII] and usually +result from a viral inflammation of the nerve within the bony canal before exiting through the stylomastoid foramen. Typically the patient has an ipsilateral loss of motor function of the whole side of the face. Not only does this produce an unusual appearance, but it also complicates chewing of food. Lacrimation and taste may not be affected if the lesion remains distal to the greater petrosal and chorda tympani branches that originate deep in the temporal bone. + + + + + + + + + + +sensory route of the maxillary [V2] and mandibular [V3] nerves may be involved. +If symptoms persist and are unresponsive to medical care, surgical exploration of the trigeminal nerve (which is not without risk) may be necessary to remove any aberrant vessels. + + + + + + + + + + + +910 +Regional Anatomy • Scalp 8 + + + +SCALP + +The scalp is the part of the head that extends from the superciliary arches anteriorly to the external occipital protuberance and superior nuchal lines posteriorly. Later-ally it continues inferiorly to the zygomatic arch. +The scalp is a multilayered structure with layers that can be defined by the word itself: + +unit is sometimes referred to as the scalp proper and is the tissue torn away during serious “scalping” injuries. + +Skin +The skin is the outer layer of the scalp (Figs. 8.70 and 8.71). It is similar structurally to skin throughout the body with the exception that hair is present on a large amount of it. + +Connective tissue (dense) + + + +■ S—skin, +■ C—connective tissue (dense), ■ A—aponeurotic layer, +■ L—loose connective tissue, and ■ P—pericranium (Fig. 8.70). + + +Deep to the skin is dense connective tissue. This layer anchors the skin to the third layer and contains the arter-ies, veins, and nerves supplying the scalp. When the scalp is cut, the dense connective tissue surrounding the vessels tends to hold cut vessels open. This results in profuse bleeding. + + + +Layers +Examining the layers of the scalp reveals that the first three layers are tightly held together, forming a single unit. This + + +Aponeurotic layer +The deepest layer of the first three layers is the aponeurotic layer. Firmly attached to the skin by the dense connective + + + + + + +Skin Connective tissue (dense) Skin Dense connective tissue Aponeurotic layer + + +Aponeurotic layer + +S + +C + + +A + + +L + +Bone Pericranium Loose connective tissue +P Fig. 8.71 Layers of the scalp. + + + +Pericranium + + +Loose connective tissue + + + + + +Fig. 8.70 SCALP. 911 +Head and Neck + + + +tissue of the second layer, this layer consists of the occipi-tofrontalis muscle, which has a frontal belly anteriorly, an occipital belly posteriorly, and an aponeurotic tendon— the epicranial aponeurosis (galea aponeurotica)—con-necting the two (Fig. 8.72). +The frontal belly of the occipitofrontalis begins anteri-orly where it is attached to the skin of the eyebrows. It passes upward, across the forehead, to become continuous with the aponeurotic tendon. +Posteriorly, each occipital belly of the occipitofrontalis arises from the lateral part of the superior nuchal line of the occipital bone and the mastoid process of the temporal bone. It also passes superiorly to attach to the aponeurotic tendon. +The occipitofrontalis muscles move the scalp, wrinkle the forehead, and raise the eyebrows. The frontal belly is + +[VII] and the posterior belly by the posterior auricular branch. + +Loose connective tissue +A layer of loose connective tissue separates the aponeurotic layer from the pericranium and facilitates movement of the scalp proper over the calvaria (Figs. 8.70 and 8.72). Because of its consistency, infections tend to localize and spread through the loose connective tissue (also see “In the clinic” on p. 878). + +Pericranium +The pericranium is the deepest layer of the scalp and is the periosteum on the outer surface of the calvaria. It is attached to the bones of the calvaria but is removable, except in the area of the sutures. + +innervated by temporal branches of the facial nerve + + + + + + + + + +Frontal belly + + + +A +Epicranial +aponeurosis Orbicularis oculi + +Occipitofrontalis + + + + + + +Occipital belly + + + + + + + +Trapezius + +B + +912 Fig. 8.72 Occipitofrontalis muscle. A. Frontal belly. B. Occipital belly. +Regional Anatomy • Scalp 8 + + + +Innervation ■ + +The supra-orbital nerve exits the orbit through the supra-orbital notch or foramen, passes through the + +Sensory innervation of the scalp is from two major sources, frontalis muscle, and continues superiorly across cranial nerves or cervical nerves, depending on whether it the scalp as far back as the vertex of the head. +is anterior or posterior to the ears and the vertex of the ■ The zygomaticotemporal nerve exits the skull + +head (Fig. 8.73), The occipitofrontalis muscle is innervated by branches of the facial nerve [VII]. + +Anterior to the ears and the vertex +Branches of the trigeminal nerve [V] supply the scalp anterior to the ears and the vertex of the head (Fig. 8.73). These branches are the supratrochlear, supra-orbital, zygomaticotemporal, and auriculotemporal nerves: + +through a foramen in the zygomatic bone and supplies the scalp over a small anterior area of the temple. +■ The auriculotemporal nerve exits from the skull, deep to the parotid gland, passes just anterior to the ear, continues superiorly anterior to the ear until nearly reaching the vertex of the head, and supplies the scalp over the temporal region and anterior to the ear to near the vertex. + + + +■ The supratrochlear nerve exits the orbit, passes through the frontalis muscle, continues superiorly across the front of the forehead, and supplies the front of the forehead near the midline. + + +Posterior to the ears and the vertex +Posterior to the ears and vertex, sensory innervation of the scalp is by cervical nerves, specifically branches from spinal + + + +Vertex + + + + + + + +Zygomaticotemporal nerves + + +Supratrochlear nerve + +Supra-orbital nerve + + + + +Greater occipital nerve + + +Third occipital nerve Auriculotemporal nerve +Lesser occipital nerve + + +C4 + +Great auricular nerve + + + + + + +Fig. 8.73 Innervation of the scalp. 913 +Head and Neck + + + +cord levels C2 and C3 (Fig. 8.73). These branches are the great auricular, the lesser occipital, the greater occipital, and the third occipital nerves: + +to the obliquus capitis inferior muscle, ascends superfi-cial to the suboccipital triangle, pierces the semispinalis capitis and trapezius muscles, and then spreads out to supply a large part of the posterior scalp as far superiorly + +■ The great auricular nerve is a branch of the cervical plexus, arises from the anterior rami of the C2 and C3 spinal nerves, ascends on the surface of the sternoclei-domastoid muscle, and innervates a small area of the scalp just posterior to the ear. +■ The lesser occipital nerve is also a branch of the + +as the vertex. +■ The third occipital nerve is a branch of the posterior ramus of the C3 spinal nerve, pierces the semispinalis capitis and trapezius muscles, and supplies a small area of the lower part of the scalp. + + + +cervical plexus, arises from the anterior ramus of the C2 spinal nerve, ascends on the posterior border of the sternocleidomastoid muscle, and supplies an area of the scalp posterior and superior to the ear. +■ The greater occipital nerve is a branch of the poste-rior ramus of the C2 spinal nerve, emerges just inferior + + +Vessels Arteries +Arteries supplying the scalp (Fig. 8.74) are branches of either the external carotid artery or the ophthalmic artery, which is a branch of the internal carotid artery. + + + + + + + + + + + + + + + +Supratrochlear artery and vein + +Supra-orbital artery and vein + + +Superficial temporal artery and vein + + +Posterior auricular vein + +Posterior auricular artery + +Occipital vein + +Occipital artery + + +External jugular vein + + +Internal jugular vein External carotid artery + + +914 Fig. 8.74 Vasculature of the scalp. +Regional Anatomy • Scalp 8 + + + + +Branches from the ophthalmic artery +The supratrochlear and supra-orbital arteries supply the anterior and superior aspects of the scalp. They branch from the ophthalmic artery while it is in the orbit, continue through the orbit, and exit onto the forehead in association with the supratrochlear and supra-orbital nerves. Like the nerves, the arteries ascend across the forehead to supply the scalp as far posteriorly as the vertex of the head. + +Branches from the external carotid artery +Three branches of the external carotid artery supply the largest part of the scalp—the superficial temporal, poste-rior auricular, and occipital arteries supply the lateral and posterior aspects of the scalp (Fig. 8.74): + +it passes through the musculature in the posterior neck to join in the formation of the plexus of veins in the suboccipital triangle. + + +In the clinic + +Scalp laceration +The scalp has an extremely rich blood supply from the external carotid arteries, so lacerations of the scalp tend to bleed profusely. Importantly, scalp bleeding is predominantly arterial, because of two reasons. First, in the erect position the venous pressure is extremely low. Second, the vessels do not retract and close when lacerated because the connective tissue in which they are found holds them open. + + + +■ The smallest branch (the posterior auricular artery) leaves the posterior aspect of the external carotid artery, passes through deeper structures, and emerges to supply an area of the scalp posterior to the ear. +■ Also arising from the posterior aspect of the external carotid artery is the occipital artery, which ascends in a posterior direction, passes through several layers of back musculature, and emerges to supply a large part of the posterior aspect of the scalp. +■ The third arterial branch supplying the scalp is the superficial temporal artery, a terminal branch of the external carotid artery that passes superiorly, just ante-rior to the ear, divides into anterior and posterior branches, and supplies almost the entire lateral aspect of the scalp. + + +Lymphatic drainage +Lymphatic drainage of the scalp generally follows the pattern of arterial distribution. +The lymphatics in the occipital region initially drain to occipital nodes near the attachment of the trapezius muscle at the base of the skull (Fig. 8.75). Further along + +Mastoid nodes + +Occipital nodes + + +Veins +Veins draining the scalp follow a pattern similar to the arteries: + + +■ The supratrochlear and supra-orbital veins drain the anterior part of the scalp from the superciliary arches to the vertex of the head (Fig. 8.74), pass inferior to the superciliary arches, communicate with the oph-thalmic veins in the orbit, and continue inferiorly to participate in the formation of the angular vein, which is the upper tributary to the facial vein. +■ The superficial temporal vein drains the entire lateral area of the scalp before passing inferiorly to join in the formation of the retromandibular vein. +■ The posterior auricular vein drains the area of the scalp posterior to the ear and eventually empties into a tributary of the retromandibular vein. +■ The occipital vein drains the posterior aspect of the scalp from the external occipital protuberance and superior nuchal lines to the vertex of the head; deeper, + + + + + + + + + + + +Submental nodes +To upper deep cervical nodes + +Submandibular nodes +Pre-auricular and parotid nodes + +Fig. 8.75 Lymphatic drainage of the scalp. 915 +Head and Neck + + + +the pathway occipital nodes drain into upper deep cervical nodes. There is also some direct drainage to upper deep cervical nodes from this part of the scalp. +Lymphatics from the upper part of the scalp drain in two directions: + + +Lesser wing of sphenoid Superior orbital fissure +Greater wing of sphenoid + + +Frontal bone Optic canal +Ethmoidal foramina +Ethmoid bone + + +■ Posterior to the vertex of the head they drain to mastoid nodes (retro-auricular/posterior auricular nodes) pos-terior to the ear near the mastoid process of the temporal bone, and efferent vessels from these nodes drain into upper deep cervical nodes. +■ Anterior to the vertex of the head they drain to pre-auricular and parotid nodes anterior to the ear on the surface of the parotid gland. + + +Finally, there may be some lymphatic drainage from the forehead to the submandibular nodes through efferent vessels that follow the facial artery. + +ORBIT + +The orbits are bilateral structures in the upper half of the face below the anterior cranial fossa and anterior to the middle cranial fossa that contain the eyeball, the optic + + + + +Zygomatic bone +Inferior orbital fissure + + +Fig. 8.76 Bones of the orbit. + + + + +Lacrimal bone Palatine bone +Maxilla + + + + +Lacrimal groove + + + +nerve, the extra-ocular muscles, the lacrimal apparatus, adipose tissue, fascia, and the nerves and vessels that supply these structures. + +bone separates the contents of the orbit from the brain in the anterior cranial fossa. +Unique features of the superior wall include: + + + + +Bony orbit +Seven bones contribute to the framework of each orbit (Fig. 8.76). They are the maxilla, zygomatic, frontal, ethmoid, lacrimal, sphenoid, and palatine bones. Together they give the bony orbit the shape of a pyramid, with its wide base opening anteriorly onto the face and its apex extending in + +■ anteromedially, the trochlear fovea, for the attachment of a pulley through which the superior oblique muscle passes, and the possible intrusion of part of the frontal sinus; +■ anterolaterally, a depression (the lacrimal fossa) for the orbital part of the lacrimal gland. + +Posteriorly, the lesser wing of the sphenoid bone com- + + + +a posteromedial direction. Completing the pyramid con-figuration are medial, lateral, superior, and inferior walls. +The apex of the pyramid-shaped bony orbit is the optic foramen, whereas the base (the orbital rim) is formed: + +pletes the roof. + +Medial wall +The medial walls of the paired bony orbits are parallel to + + + + +■ superiorly by the frontal bone, +■ medially by the frontal process of the maxilla, +■ inferiorly by the zygomatic process of the maxilla and the zygomatic bone, and +■ laterally by the zygomatic bone, the frontal process of the zygomatic bone, and the zygomatic process of the frontal bone. + +each other and each consists of four bones—the maxilla, lacrimal, ethmoid, and sphenoid bones (Fig. 8.76). +The largest contributor to the medial wall is the orbital plate of the ethmoid bone. This part of the ethmoid bone contains collections of ethmoidal cells, which are clearly visible in a dried skull. +Also visible, at the junction between the roof and the medial wall, usually associated with the frontoethmoidal + + + + +Roof +The roof (superior wall) of the bony orbit is made up of the orbital part of the frontal bone with a small contribu- +916 tion from the sphenoid bone (Fig. 8.76). This thin plate of + +suture, are the anterior and posterior ethmoidal foramina. The anterior and posterior ethmoidal nerves and vessels leave the orbit through these openings. +Anterior to the ethmoid bone is the small lacrimal bone, and completing the anterior part of the medial wall is the +Regional Anatomy • Orbit 8 + + + +frontal process of the maxilla. These two bones participate in the formation of the lacrimal groove, which contains the lacrimal sac and is bound by the posterior lacrimal crest (part of the lacrimal bone) and the anterior lacri-mal crest (part of the maxilla). +Posterior to the ethmoid bone the medial wall is com-pleted by a small part of the sphenoid bone, which forms a part of the medial wall of the optic canal. + +Floor +The floor (inferior wall) of the bony orbit, which is also the roof of the maxillary sinus, consists primarily of the orbital surface of the maxilla (Fig. 8.76), with small con-tributions from the zygomatic and palatine bones. +Beginning posteriorly and continuing along the lateral boundary of the floor of the bony orbit is the inferior orbital fissure. Beyond the anterior end of the fissure the zygomatic bone completes the floor of the bony orbit. +Posteriorly, the orbital process of the palatine bone makes a small contribution to the floor of the bony orbit near the junction of the maxilla, ethmoid, and sphenoid bones. + +Lateral wall +The lateral wall of the bony orbit consists of contribu-tions from two bones—anteriorly, the zygomatic bone and posteriorly, the greater wing of the sphenoid bone (Fig. 8.76). The superior orbital fissure is between the greater wing of the sphenoid and the lesser wing of the sphenoid that forms part of the roof. + + +Eyelids +The upper and lower eyelids are anterior structures that, when closed, protect the surface of the eyeball. +The space between the eyelids, when they are open, is the palpebral fissure. +The layers of the eyelids, from anterior to posterior, consist of skin, subcutaneous tissue, voluntary muscle, the orbital septum, the tarsus, and conjunctiva (Fig. 8.77). +The upper and lower eyelids are basically similar in structure except for the addition of two muscles in the upper eyelid. + +Skin and subcutaneous tissue +The skin of the eyelids is not particularly substantial, and only a thin layer of connective tissue separates the skin from the underlying voluntary muscle layer (Fig. 8.77). The thin layer of connective tissue and its loose arrange-ment account for the accumulation of fluid (blood) when an injury occurs. + +Orbicularis oculi +The muscle fibers encountered next in an anteroposterior direction through the eyelid belong to the palpebral part of the orbicularis oculi (Fig. 8.77). This muscle is part of the larger orbicularis oculi muscle, which consists primar-ily of two parts—an orbital part, which surrounds the orbit, and the palpebral part, which is in the eyelids. The orbicularis oculi is innervated by the facial nerve [VII] and closes the eyelids. + + + + + +In the clinic + +Orbital fracture +Fractures of the orbit are not uncommon and may involve the orbital margins with extension into the maxilla, frontal, and zygomatic bones. These fractures are often part of complex facial fractures. Fractures within the orbit frequently occur within the floor and the medial wall; however, superior and lateral wall fractures also occur. Inferior orbital floor fractures are one of the commonest types of injuries. These fractures may drag the inferior oblique muscle and associated tissues into the fracture line. In these instances, patients may have upward gaze failure (upward gaze diplopia) in the affected eye. Medial wall fractures characteristically show air within the orbit in radiographs. This is due to fracture of the ethmoidal labyrinth, permitting direct continuity between the orbit and the ethmoidal paranasal sinuses. Occasionally, patients feel a full sensation within the orbit when blowing the nose. + + +Periosteum + + +Orbicularis oculi muscle +Orbital septum +Tendon of levator palpebrae superioris muscle +Superior conjunctival fornix + +Conjunctiva Tarsus Sebaceous gland of eyelash + + + +Tarsal gland + + +Fig. 8.77 Eyelids. + +Levator palpebrae superioris muscle + + + + + + + + + + + + + + + + + +Superior tarsal muscle (smooth muscle) + +917 +Head and Neck + + + +The palpebral part is thin and anchored medially by the medial palpebral ligament (Fig. 8.78), which attaches to the anterior lacrimal crest and laterally blends with fibers from the muscle in the lower eyelid at the lateral palpebral ligament (Fig. 8.78). +A third part of the orbicularis oculi muscle that can be identified consists of fibers on the medial border, which pass deeply to attach to the posterior lacrimal crest. These fibers form the lacrimal part of the orbicularis oculi, which may be involved in the drainage of tears. + +Orbital septum +Deep to the palpebral part of the orbicularis oculi is an extension of periosteum into both the upper and lower eyelids from the margin of the orbit (Fig. 8.79). This is the orbital septum, which extends downward into the upper eyelid and upward into the lower eyelid and is continuous with the periosteum outside and inside the orbit (Fig. 8.79). The orbital septum attaches to the tendon of the levator palpebrae superioris muscle in the upper eyelid and attaches to the tarsus in the lower eyelid. + +Tarsus and levator palpebrae superioris +Providing major support for each eyelid is the tarsus (Fig. 8.80). There is a large superior tarsus in the upper eyelid and a smaller inferior tarsus in the lower eyelid (Fig. 8.80). These plates of dense connective tissue are attached medially to the anterior lacrimal crest of the maxilla by the medial palpebral ligament and laterally to the orbital tubercle on the zygomatic bone by the lateral palpebral ligament. + + + + +Periosteum + + + + +Orbital septum +Tendon of levator palpebrae superioris muscle + + + + + + + + + + + +Orbital septum + + + + +Periosteum + + + + +Fig. 8.79 Orbital septum. + +Tendon of levator palpebrae superioris muscle + +Orbital septum Anterior lacrimal crest + + + + + + + + +Orbicularis oculi muscle + +Orbital part + +Palpebral part + +Medial palpebral ligament + +Superior tarsus + +Lateral palpebral ligament + + + +Inferior tarsus + + + +Lateral palpebral ligament + + + +918 Fig. 8.78 Orbicularis oculi muscle. + + + +Orbital septum +Medial palpebral ligament + +Fig. 8.80 Tarsal plates. +Regional Anatomy • Orbit 8 + + + +Although the tarsal plates in the upper and lower eyelids are generally similar in structure and function, there is one unique difference. Associated with the tarsus in the upper eyelid is the levator palpebrae superioris muscle (Fig. 8.80), which raises the eyelid. Its origin is from the posterior part of the roof of the orbit, just superior to + +inflammation of either of these is a stye and is on the edge of the eyelid. + +Vessels +The arterial supply to the eyelids is from the numerous vessels in the area (Fig. 8.81). They include: + + + +the optic foramen, and it inserts into the anterior surface of the superior tarsus, with the possibility of a few fibers attaching to the skin of the upper eyelid. It is innervated by the oculomotor nerve [III]. +In companion with the levator palpebrae superioris muscle is a collection of smooth muscle fibers passing from the inferior surface of the levator to the upper edge of the superior tarsus (see Fig. 8.77). Innervated by postgangli-onic sympathetic fibers from the superior cervical ganglion, + + +■ the supratrochlear, supra-orbital, lacrimal, and dorsal nasal arteries from the ophthalmic artery; +■ the angular artery from the facial artery; +■ the transverse facial artery from the superficial temporal artery; and +■ branches from the superficial temporal artery itself. + +Venous drainage follows an external pattern through + + + +this muscle is the superior tarsal muscle. +Loss of function of either the levator palpebrae superi-oris muscle or the superior tarsal muscle results in a ptosis or drooping of the upper eyelid. + +Conjunctiva +The structure of the eyelid is completed by a thin mem-brane (the conjunctiva), which covers the posterior surface of each eyelid (see Fig. 8.77). This membrane covers the full extent of the posterior surface of each eyelid before reflecting onto the outer surface (sclera) of the eyeball. It attaches to the eyeball at the junction between the sclera and the cornea. With this membrane in place, a conjunctival sac is formed when the eyelids are closed, and the upper and lower extensions of this sac are the superior and inferior conjunctival fornices (Fig. 8.77). + +Glands +Embedded in the tarsal plates are tarsal glands (see Fig. 8.77), which empty onto the free margin of each eyelid. These glands are modified sebaceous glands and secrete an oily substance that increases the viscosity of the tears and decreases the rate of evaporation of tears from the surface of the eyeball. Blockage and inflammation of a tarsal gland is a chalazion and is on the inner surface of the eyelid. +The tarsal glands are not the only glands associated with the eyelids. Associated with the eyelash follicles are sebaceous and sweat glands (see Fig. 8.77). Blockage and + +veins associated with the various arteries and an internal pattern moving into the orbit through connections with the ophthalmic veins. +Lymphatic drainage is primarily to the parotid nodes, with some drainage from the medial corner of the eye along lymphatic vessels associated with the angular and facial arteries to the submandibular nodes. + +Supratrochlear artery and vein +Supra-orbital artery and vein + +Lacrimal artery + + + +Superficial temporal artery and vein + + + +Transverse facial artery + + + +Infra-orbital artery +Angular artery and vein + +Fig. 8.81 Vasculature of the eyelids. + + + + + + + + + + +919 +Head and Neck + + + +Innervation +Innervation of the eyelids includes both sensory and motor components. +The sensory nerves are all branches of the trigeminal nerve [V] (Fig. 8.82). Palpebral branches arise from: + +In the clinic + +Horner’s syndrome +Horner’s syndrome is caused by any lesion that leads to a loss of sympathetic function in the head. It is characterized by three typical features: + + + + +■ the supra-orbital, supratrochlear, infratrochlear, and lacrimal branches of the ophthalmic nerve [V1]; and +■ the infra-orbital branch of the maxillary nerve [V2]. + +Motor innervation is from: + +■ the facial nerve [VII], which innervates the palpebral part of the orbicularis oculi; +■ the oculomotor nerve [III], which innervates the levator palpebrae superioris; and +■ sympathetic fibers, which innervate the superior tarsal muscle. + +■ pupillary constriction due to paralysis of the dilator pupillae muscle, +■ partial ptosis (drooping of the upper eyelid) due to paralysis of the superior tarsal muscle, and +■ absence of sweating on the ipsilateral side of the face and the neck due to absence of innervation of the sweat glands. + +Secondary changes may also include: + +■ ipsilateral vasodilation due to loss of the normal sympathetic control of the subcutaneous blood vessels, and +■ enophthalmos (sinking of the eye)—believed to result from paralysis of the orbitalis muscle, although this is an uncommon feature of Horner’s syndrome. + + + +Loss of innervation of the orbicularis oculi by the facial nerve [VII] causes an inability to close the eyelids tightly and the lower eyelid droops away, resulting in a spillage of tears. +Loss of innervation of the levator palpebrae superioris by the oculomotor nerve causes an inability to open the superior eyelid voluntarily, producing a complete ptosis. +Loss of innervation of the superior tarsal muscle by sympathetic fibers causes a constant partial ptosis. + + + + +Infratrochlear nerve Supratrochlear nerve +Supra-orbital nerve + + + + + + +Lacrimal nerve + + +The orbitalis muscle spans the inferior orbital fissure and helps maintain the forward position of orbital contents. +The commonest cause for Horner’s syndrome is a tumor eroding the cervicothoracic ganglion, which is typically an apical lung tumor. +Surgically induced Horner’s syndrome +A surgically induced Horner’s syndrome may be necessary for patients who suffer severe hyperhidrosis (sweating). This often debilitating condition may be so severe that patients are confined to their home for fear of embarrassment. Treatment is relatively straightforward. The patient is anesthetized and a bifurcate endotracheal tube is placed into the left and right main bronchi. A small incision is made in the intercostal space on the appropriate side, and a surgically induced pneumothorax is created. The patient is ventilated through the contralateral lung. +Using an endoscope the apex of the thoracic cavity can be viewed from inside and the cervicothoracic ganglion readily identified. Obliterative techniques include thermocoagulation and surgical excision. After the ganglion has been destroyed, the endoscope is removed, the lung is reinflated, and the small hole is sutured. + + + + + + + + + +Infra-orbital nerve + +920 Fig. 8.82 Innervation of the eyelids. +Regional Anatomy • Orbit 8 + + + + +Lacrimal apparatus +The lacrimal apparatus is involved in the production, movement, and drainage of fluid from the surface of the eyeball. It is made up of the lacrimal gland and its ducts, the lacrimal canaliculi, the lacrimal sac, and the naso-lacrimal duct. + +■ The larger orbital part is in a depression, the lacrimal fossa, in the frontal bone. +■ The smaller palpebral part is inferior to the levator palpebrae superioris in the superolateral part of the eyelid. + +Numerous ducts empty the glandular secretions into + + + +The lacrimal gland is anterior in the superolateral region of the orbit (Fig. 8.83) and is divided into two parts by the levator palpebrae superioris (Fig. 8.84): + + + + +Tendon of levator palpebrae superioris muscle + +Lacrimal gland + + + +Medial + +Lacrimal canaliculi + +Lacrimal sac + +the lateral part of the superior fornix of the conjunctiva. Fluid is continually being secreted by the lacrimal gland +and moved across the surface of the eyeball from lateral to medial as the eyelids blink. +The fluid accumulates medially in the lacrimal lake and is drained from the lake by the lacrimal canaliculi, one canaliculus associated with each eyelid (Fig. 8.83). The lacrimal punctum is the opening through which fluid enters each canaliculus. +Passing medially, the lacrimal canaliculi eventually join the lacrimal sac between the anterior and posterior lacri-mal crests, posterior to the medial palpebral ligament and anterior to the lacrimal part of the orbicularis oculi muscle (Figs. 8.85 and 8.86). When the orbicularis oculi muscle contracts during blinking, the small lacrimal part of the muscle may dilate the lacrimal sac and draw tears into it through the canaliculi from the conjunctival sac. + + + +Puncta +Nasolacrimal duct + +Fig. 8.83 Lacrimal gland, anterior view. + + +Lacrimal vessels and nerve Puncta Lacrimal canaliculi +Orbital part of lacrimal gland + + + + +Orbital septum + +Tendon of levator palpebrae +superioris + +Palpebral part of lacrimal gland + + + +Nasolacrimal duct +Lacrimal canaliculi Lacrimal sac + +Fig. 8.84 Lacrimal gland and levator palpebrae superioris. Fig. 8.85 The lacrimal sac. 921 +Head and Neck + + + + +Innervation +The innervation of the lacrimal gland involves three differ-ent components (Fig. 8.87). + +Sensory innervation +Sensory neurons from the lacrimal gland return to the CNS through the lacrimal branch of the ophthalmic nerve [V1]. + +Secretomotor (parasympathetic) innervation +Secretomotor fibers from the parasympathetic part of the autonomic division of the PNS stimulate fluid secretion + + + + +Anterior Periosteum +Anterior lacrimal crest +Lacrimal sac + +Medial palpebral ligament + + +Lateral + + +Lacrimal part of orbicularis oculi muscle + +Orbital septum + +from the lacrimal gland. These preganglionic parasympa-thetic neurons leave the CNS in the facial nerve [VII], enter the greater petrosal nerve (a branch of the facial nerve [VII]), and continue with this nerve until it becomes the nerve of the pterygoid canal (Fig. 8.87). +The nerve of the pterygoid canal eventually joins the pterygopalatine ganglion where the preganglionic para-sympathetic neurons synapse on postganglionic parasym-pathetic neurons. The postganglionic neurons join the maxillary nerve [V2] and continue with it until the zygo-matic nerve branches from it, and travel with the zygomatic nerve until it gives off the zygomaticotemporal nerve, which eventually distributes postganglionic parasympa-thetic fibers in a small branch that joins the lacrimal nerve. The lacrimal nerve passes to the lacrimal gland. + +Sympathetic innervation +Sympathetic innervation of the lacrimal gland follows a similar path as parasympathetic innervation. Postgangli-onic sympathetic fibers originating in the superior cervical ganglion travel along the plexus surrounding the internal carotid artery (Fig. 8.87). They leave this plexus as the deep petrosal nerve and join the parasympathetic fibers in the nerve of the pterygoid canal. Passing through the pterygo-palatine ganglion, the sympathetic fibers from this point onward follow the same path as the parasympathetic fibers to the lacrimal gland. + +Vessels + +Posterior Posterior lacrimal crest The arterial supply to the lacrimal gland is by branches + + +Fig. 8.86 Position of lacrimal sac. + +from the ophthalmic artery and venous drainage is through the ophthalmic veins. + + + + + +Lacrimal gland + +Lacrimal nerve + + + +Zygomaticotemporal nerve + +Zygomaticofacial nerve +Foramen rotundum + +Maxillary nerve [V2] Branch of zygomaticotemporal nerve Zygomatic nerve Pterygoid canal + + + + +Pterygopalatine ganglion + + +Sensory fibers +Sympathetic postganglionic fibers Parasympathetic preganglionic fibers Parasympathetic postganglionic fibers + + + + + + +Nerve of pterygoid canal + +Greater petrosal nerve Deep petrosal nerve + +Internal carotid artery + +Sympathetic plexus + + +922 Fig. 8.87 Innervation of the lacrimal gland. +Regional Anatomy • Orbit 8 + + + +Fissures and foramina +Numerous structures enter and leave the orbit through a variety of openings (Fig. 8.88). + +Optic canal +When the bony orbit is viewed from an anterolateral posi-tion, the round opening at the apex of the pyramidal-shaped orbit is the optic canal, which opens into the middle cranial fossa and is bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid. Passing through the optic canal are the optic nerve and the ophthalmic artery (Fig. 8.89). + + +Lesser wing of sphenoid Superior orbital fissure +Greater wing of sphenoid + +Frontal bone Optic canal +Ethmoidal foramina +Ethmoid bone +Lacrimal bone + + + +Superior orbital fissure +Just lateral to the optic canal is a triangular-shaped gap between the roof and lateral wall of the bony orbit. This is the superior orbital fissure and allows structures to pass between the orbit and the middle cranial fossa (Fig. 8.88). Passing through the superior orbital fissure are the superior and inferior branches of the oculomotor nerve [III], the trochlear nerve [IV], the abducent nerve [VI], the lacrimal, frontal, and nasociliary branches of the ophthalmic nerve [V1], and the superior ophthalmic vein +(Fig. 8.89). + + + + + + + +Zygomatic bone Nasolacrimal +Inferior orbital fissure canal +Palatine bone +Infra-orbital groove +Maxilla + +Fig. 8.88 Openings into the bony orbit. + + +Inferior orbital fissure +Separating the lateral wall of the orbit from the floor of the orbit is a longitudinal opening, the inferior orbital fissure (Fig. 8.88). Its borders are the greater wing of the sphenoid + + +Frontal branch of the ophthalmic nerve [V1] Trochlear nerve [IV] +Optic nerve + + +Lacrimal branch of the ophthalmic nerve [V1] + + +Superior ophthalmic vein + +Superior orbital fissure + +Abducent nerve [VI] + +Optic canal + +Ophthalmic artery + +Superior branch of oculomotor nerve [III] + + +Nasociliary branch of ophthalmic nerve [V1] + + +Inferior branch of oculomotor nerve [III] + + + +Inferior orbital fissure + + + + +Lateral + + +Fig. 8.89 Optic canal and superior orbital fissure. + +Inferior ophthalmic vein + + + + +Medial + + +923 +Head and Neck + + + +and the maxilla, palatine, and zygomatic bones. This long fissure allows communication between: + + +Periorbita +Dura mater + + +■ the orbit and the pterygopalatine fossa posteriorly, +■ the orbit and the infratemporal fossa in the middle, and Periosteum ■ the orbit and the temporal fossa posterolaterally. + +Passing through the inferior orbital fissure are the maxillary nerve [V2] and its zygomatic branch, the infra-orbital vessels, and a vein communicating with the ptery-goid plexus of veins. + + +Infra-orbital foramen +Beginning posteriorly and crossing about two-thirds of the inferior orbital fissure, a groove (the infra-orbital groove) is encountered, which continues anteriorly across the floor of the orbit (Fig. 8.88). This groove connects with the infra-orbital canal that opens onto the face at the infra-orbital foramen. +The infra-orbital nerve, part of the maxillary nerve [V2], and vessels pass through this structure as they exit onto the face. + +Other openings +Associated with the medial wall of the bony orbit are several smaller openings (Fig. 8.88). +The anterior and posterior ethmoidal foramina are + + +Orbital septum + +A + + + + +Common tendinous ring + + +Inferior orbital fissure + + + +B + + + + +Superior orbital fissure +Optic canal + + + +at the junction between the superior and medial walls. These openings provide exits from the orbit into the ethmoid bone for the anterior and posterior ethmoidal nerves and vessels. +Completing the openings on the medial wall is a canal in the lower part of the wall anteriorly. Clearly visible is the depression for the lacrimal sac formed by the lacrimal bone and the frontal process of the maxilla. This depression is continuous with the nasolacrimal canal, which leads to the inferior nasal meatus. Contained within the nasolacri-mal canal is the nasolacrimal duct, a part of the lacrimal apparatus. + + +Fascial specializations Periorbita +The periosteum lining the bones that form the orbit is the periorbita (Fig. 8.90A). It is continuous at the margins of + + +Fig. 8.90 Periorbita. A. Lateral view. B. Common tendinous ring. + + + + + + + +the orbit with the periosteum on the outer surface of the skull and sends extensions into the upper and lower eyelids (the orbital septa). +At the various openings where the orbit communicates with the cranial cavity the periorbita is continuous with the periosteal layer of dura mater. In the posterior part of the orbit, the periorbita thickens around the optic canal and the central part of the superior orbital fissure. This is the point of origin of the four rectus muscles and is the common tendinous ring. + + + + + + + +924 +Regional Anatomy • Orbit 8 + + + + +Fascial sheath of the eyeball +The fascial sheath of the eyeball (bulbar sheath) is a layer of fascia that encloses a major part of the eyeball (Figs. 8.91 and 8.92): + +■ The medial check ligament is an extension from the fascia covering the medial rectus muscle and attaches immediately posterior to the posterior lacrimal crest of the lacrimal bone. +■ The lateral check ligament is an extension from the + + +■ Posteriorly, it is firmly attached to the sclera (the white part of the eyeball) around the point of entrance of the optic nerve into the eyeball. +■ Anteriorly, it is firmly attached to the sclera near the edge of the cornea (the clear part of the eyeball). +■ Additionally, as the muscles approach the eyeball, the investing fascia surrounding each muscle blends with the fascial sheath of the eyeball as the muscles pass through and continue to their point of attachment. + +fascia covering the lateral rectus muscle and is attached to the orbital tubercle of the zygomatic bone. + +Functionally, the positioning of these ligaments seems to restrict the medial and lateral rectus muscles, thus the names of the fascial specializations. + +Muscles +There are two groups of muscles within the orbit: + + + + +A specialized lower part of the fascial sheath of the eyeball is the suspensory ligament (Figs. 8.91 and 8.92), which supports the eyeball. This “sling-like” structure is made up of the fascial sheath of the eyeball and contribu-tions from the two inferior ocular muscles and the medial and lateral ocular muscles. + +■ extrinsic muscles of eyeball (extra-ocular muscles) involved in movements of the eyeball or raising upper eyelids, and +■ intrinsic muscles within the eyeball, which control the shape of the lens and size of the pupil. + + + +Check ligaments of the medial and lateral rectus muscles +Other fascial specializations in the orbit are the check liga-ments (Fig. 8.92). These are expansions of the investing fascia covering the medial and lateral rectus muscles, which attach to the medial and lateral walls of the bony orbit: + + + +Lateral rectus muscle + + +Check ligament of lateral rectus muscle +Suspensory ligament + + +Medial rectus muscle + + + + + +Check ligament of medial rectus muscle +Inferior rectus muscle + + + + + +Periosteum + + + +Fascial sheath + + +Periorbita Fascial sheath +Superior rectus muscle + +A Inferior oblique muscle + + +Periosteum +Suspensory ligament + + +Lacrimal sac + + + + + +Suspensory ligament + + + + + + + + +Orbital septum + +Suspensory ligament + + + + + + + + + +Inferior rectus muscle +Inferior oblique muscle + + +Medial check ligament + +Fascial sheath + +Medial rectus muscle + +B + +Lateral check ligament + +Periorbita + +Fascial sheath + +Lateral rectus muscle + + +Fig. 8.91 Fascial sheath of the eyeball. Fig. 8.92 Check ligaments. A. Anterior view. B. Superior view. 925 +Head and Neck + + + +Table 8.8 + +Muscle + +Extrinsic (extra-ocular) muscles + +Origin Insertion Innervation Function + + + +Levator palpebrae superioris + +Superior rectus + +Inferior rectus + +Medial rectus + +Lateral rectus + +Superior oblique + +Inferior oblique + +Lesser wing of sphenoid anterior to optic canal + +Superior part of common tendinous ring +Inferior part of common tendinous ring +Medial part of common tendinous ring +Lateral part of common tendinous ring +Body of sphenoid, superior and medial to optic canal +Medial floor of orbit posterior to rim; maxilla lateral to nasolacrimal groove + +Anterior surface of tarsal plate; a few fibers to skin and superior conjunctival fornix +Anterior half of eyeball superiorly +Anterior half of eyeball inferiorly +Anterior half of eyeball medially +Anterior half of eyeball laterally +Outer posterior quadrant of eyeball (superior surface) +Outer posterior quadrant of eyeball (inferior surface) + +Oculomotor nerve [III]—superior branch + +Oculomotor nerve [III]—superior branch +Oculomotor nerve [III]—inferior branch +Oculomotor nerve [III]—inferior branch +Abducent nerve [VI] + +Trochlear nerve [IV] + +Oculomotor nerve [III]—inferior branch + +Elevation of upper eyelid + + +Elevation, adduction, medial rotation of eyeball +Depression, adduction, lateral rotation of eyeball +Adduction of eyeball + +Abduction of eyeball + +Depression, abduction, internal rotation of eyeball +Elevation, abduction, external rotation of eyeball + + + + + +The extrinsic muscles include the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique. +The intrinsic muscles include the ciliary muscle, the + + +Superior + +Elevation +External rotation Internal rotation + + + +sphincter pupillae, and the dilator pupillae. + +Extrinsic muscles +Of the seven muscles in the extrinsic group of muscles, one raises the eyelids, whereas the other six move the eyeball itself (Table 8.8). +The movements of the eyeball, in three dimensions, (Fig. 8.93) are: + + +A b d u +Lateral c t i o n + + +A d d u +c Medial t +i o n + + + +■ elevation—moving the pupil superiorly, ■ depression—moving the pupil inferiorly, ■ abduction—moving the pupil laterally, ■ adduction—moving the pupil medially, +■ internal rotation (intorsion)—rotating the upper part of the pupil medially (or toward the nose), and +■ external rotation (extorsion)—rotating the upper part of the pupil laterally (or toward the temple). + +Depression + +Inferior + +Fig. 8.93 Movements of the eyeball. + + + +The axis of each orbit is directed slightly laterally from back to front, but each eyeball is directed anteriorly (Fig. 8.94). Therefore the pull of some muscles has multiple effects on the movement of the eyeball, whereas that of others has a single effect. + +Medial + + + + +Axis of eyeball + + + +Levator palpebrae superioris +Levator palpebrae superioris raises the upper eyelid (Table 8.8). It is the most superior muscle in the orbit, originating +926 from the roof, just anterior to the optic canal on the inferior + + + +Axis of orbit + +Fig. 8.94 Axes of the eyeball and orbit. +Regional Anatomy • Orbit 8 + + + +surface of the lesser wing of the sphenoid (Fig. 8.95B). Its primary point of insertion is into the anterior surface of the superior tarsus, but a few fibers also attach to the skin of the upper eyelid and the superior conjunctival fornix. +Innervation is by the superior branch of the oculomotor nerve [III]. +Contraction of the levator palpebrae superioris raises the upper eyelid. +A unique feature of the levator palpebrae superioris is that a collection of smooth muscle fibers passes from its inferior surface to the upper edge of the superior tarsus (see Fig. 8.77). This group of smooth muscle fibers (the superior tarsal muscle) help maintain eyelid elevation and are innervated by postganglionic sympathetic fibers from the superior cervical ganglion. +Loss of oculomotor nerve [III] function results in com-plete ptosis or drooping of the superior eyelid, whereas loss + +of sympathetic innervation to the superior tarsal muscle results in partial ptosis. + +Rectus muscles +Four rectus muscles occupy medial, lateral, inferior, and superior positions as they pass from their origins posteriorly to their points of attachment on the anterior half of the eyeball (Fig. 8.95 and Table 8.8). They originate as a group from a common tendinous ring at the apex of the orbit and form a cone of muscles as they pass forward to their attach-ment on the eyeball. + +Superior and inferior rectus muscles +The superior and inferior rectus muscles have complicated actions because the apex of the orbit, where the muscles originate, is medial to the central axis of the eyeball when looking directly forward: + + +Trochlea Superior oblique Levator palpebrae superioris + +Superior rectus + +Medial rectus + +Superior oblique +Medial rectus +Superior rectus + + +Lateral rectus + + + + + + +Inferior oblique + +B + +A + + +Lateral rectus +Inferior rectus + + + +Superior oblique + +Superior rectus + +Optic nerve + +Lateral rectus + + +Inferior rectus + +Medial rectus + +C + +Fig. 8.95 Muscles of the eyeball. A. Superior view. B. Lateral view. C. Coronal magnetic resonance image through the eye. 927 +Head and Neck + + + +■ The superior rectus originates from the superior part of the common tendinous ring above the optic canal. +■ The inferior rectus originates from the inferior part of the common tendinous ring below the optic canal (Fig. 8.96). + +As these muscles pass forward in the orbit to attach to + + +Medial and lateral rectus muscles +The orientation and actions of the medial and lateral rectus muscles are more straightforward than those of the superior and inferior rectus muscles. +The medial rectus originates from the medial part of the common tendinous ring medial to and below the + +the anterior half of the eyeball, they are also directed later-ally (Fig. 8.95). Because of these orientations: + +optic canal, whereas the lateral rectus originates from the lateral part of the common tendinous ring as the + + +■ Contraction of the superior rectus elevates, adducts, and internally rotates the eyeball (Fig. 8.97A). +■ Contraction of the inferior rectus depresses, adducts, and externally rotates the eyeball (Fig. 8.97A). + +common tendinous ring bridges the superior orbital fissure (Fig. 8.96). +The medial and lateral rectus muscles pass forward and attach to the anterior half of the eyeball (Fig. 8.95). + + + +The superior branch of the oculomotor nerve [III] innervates the superior rectus, and the inferior branch of the oculomotor nerve [III] innervates the inferior rectus. To isolate the function of and to test the superior and inferior rectus muscles, a patient is asked to track a physi-cian’s finger laterally and then either upward or downward (Fig. 8.97B). The first movement brings the axis of the eyeball into alignment with the long axis of the superior and inferior rectus muscles. Moving the finger upward tests the superior rectus muscle and moving it downward tests +the inferior rectus muscle (Fig. 8.97B). + + + + + + +Abduction + +Lateral + + + +A + + + +Inferior oblique + + +Lateral rectus + + +Superior oblique + + +Elevation + + + + + + + + + + +Depression + + + +Superior rectus + + +Medial rectus + + +Inferior rectus + + + + + + +Adduction + +Medial + + + + + + + +Superior orbital fissure Lacrimal nerve +Frontal nerve Trochlear +nerve [IV] + + + + + +Superior rectus +Levator palpebrae superioris +Optic nerve + +Superior oblique + +Ophthalmic artery Medial rectus +Superior division of oculomotor nerve [III] Nasociliary nerve +Abducent nerve [VI] + +Inferior division of oculomotor nerve [III] + +Inferior rectus + +Inferior ophthalmic vein + +Inferior orbital fissure + +Lateral rectus + + +Muscle tested + + +Superior rectus + + + +Inferior rectus + + + +Lateral rectus + + + +Medial rectus + + + +Inferior oblique + + + +Superior oblique + +B + +Direction to move eye when testing muscle + +Look laterally and upward + + +Look laterally and downward + + +Look laterally + + + +Look medially + + +Look medially and upward + + +Look medially and downward + + + +Lateral Medial + +928 Fig. 8.96 Origins of muscles of the eyeball, coronal view. + + +Fig. 8.97 Actions of muscles of the eyeball. A. Action of individual muscles (anatomical action). B. Movement of eye when testing specific muscle (clinical testing). +Regional Anatomy • Orbit 8 + + + +Contraction of medial rectus adducts the eyeball, whereas contraction of lateral rectus abducts the eyeball (Fig. 8.97A). +The inferior branch of the oculomotor nerve [III] inner-vates the medial rectus, and the abducent nerve [VI] innervates the lateral rectus. +To isolate the function of and test the medial and lateral rectus muscles, a patient is asked to track a physician’s finger medially and laterally, respectively, in the horizontal plane (Fig. 8.97B). + +Oblique muscles +The oblique muscles are in the superior and inferior parts of the orbit, do not originate from the common tendinous ring, are angular in their approaches to the eyeball, and, unlike the rectus muscles, attach to the posterior half of the eyeball (Table 8.8). + +Superior oblique +The superior oblique arises from the body of the sphenoid, superior and medial to the optic canal and medial to the origin of the levator palpebrae superioris (Figs. 8.95 and 8.96). It passes forward, along the medial border of the roof of the orbit, until it reaches a fibrocartilaginous pulley (the trochlea), which is attached to the trochlear fovea of the frontal bone. +The tendon of the superior oblique passes through the trochlea and turns laterally to cross the eyeball in a pos-terolateral direction. It continues deep to the superior rectus muscle and inserts into the outer posterior quadrant of the eyeball. +Contraction of the superior oblique therefore directs the pupil down and out (Fig. 8.97A). +The trochlear nerve [IV] innervates the superior oblique along its superior surface. +To isolate the function of and to test the superior oblique muscle, a patient is asked to track a physician’s finger medi-ally to bring the axis of the tendon of the muscle into + + +In the clinic + +Examination of the eye +Examination of the eye includes assessment of the visual capabilities, the extrinsic musculature and its function, and disease processes that may affect the eye in isolation or as part of the systemic process. +Examination of the eye includes tests for visual acuity, astigmatism, visual fields, and color interpretation (to exclude color blindness) in a variety of circumstances. The physician also assesses the retina, the optic nerve and its coverings, the lens, and the cornea. + +alignment with the axis of the eyeball, and then to look down, which tests the muscle (Fig. 8.97B). + +Inferior oblique +The inferior oblique is the only extrinsic muscle that does not take origin from the posterior part of the orbit. It arises from the medial side of the floor of the orbit, just posterior to the orbital rim, and is attached to the orbital surface of the maxilla just lateral to the nasolacrimal groove (Fig. 8.95). +The inferior oblique crosses the floor of the orbit in a posterolateral direction between the inferior rectus and the floor of the orbit, before inserting into the outer posterior quadrant just under the lateral rectus. +Contraction of the inferior oblique directs the pupil up and out (Fig. 8.97A). +The inferior branch of the oculomotor nerve innervates the inferior oblique. +To isolate the function of and to test the inferior oblique muscle, a patient is asked to track a physician’s finger medi-ally to bring the axis of the eyeball into alignment with the axis of the muscle and then to look up, which tests the muscle (Fig. 8.97B). + +Extrinsic muscles and eyeball movements +Six of the seven extrinsic muscles of the orbit are directly involved in movements of the eyeball. +For each of the rectus muscles, the medial, lateral, inferior, and superior, and the superior and inferior obliques, a specific action or group of actions can be described (Table 8.8). However, these muscles do not act in isolation. They work as teams of muscles in the coordinated movement of the eyeball to position the pupil as needed. +For example, although the lateral rectus is the muscle primarily responsible for moving the eyeball laterally, it is assisted in this action by the superior and inferior oblique muscles. + + + + +The extrinsic muscles are supplied by the abducent nerve [VI], the trochlear nerve [IV], and the oculomotor nerve [III]. +The extrinsic muscles work synergistically to provide appropriate and conjugate eye movement: + +■ lateral rectus—abducent nerve [VI], +■ superior oblique—trochlear nerve [IV], and ■ remainder—oculomotor nerve [III]. + +The eye may be affected in systemic diseases. Diabetes mellitus typically affects the eye and may cause cataracts, +(continues) 929 +Head and Neck + + + +In the clinic—cont’d + +macular disease, and retinal hemorrhage, all impairing vision. +Occasionally unilateral paralysis of the extra-ocular muscles occurs and is due to brainstem injury or direct nerve injury, which may be associated with tumor compression or trauma. The paralysis of a muscle is easily demonstrated when the patient attempts to move the eye in the direction associated with normal action of that muscle. Typically the patient complains of double vision (diplopia). +Loss of innervation of the muscles around the eye +Loss of innervation of the orbicularis oculi by the facial nerve [VII] causes an inability to close the eyelids tightly, allowing the lower eyelid to droop away causing spillage of tears. + + + +This loss of tears allows drying of the conjunctiva, which may ulcerate, so allowing secondary infection. +Loss of innervation of the levator palpebrae superioris by oculomotor nerve [III] damage causes an inability of the superior eyelid to elevate, producing a complete ptosis. Usually, oculomotor nerve [III] damage is caused by severe head injury. +Loss of innervation of the superior tarsal muscle by sympathetic fibers causes a constant partial ptosis. Any lesion along the sympathetic trunk can induce this. An apical pulmonary malignancy should always be suspected because the ptosis may be part of Horner’s syndrome (see “In the clinic” on p. 920). + + + + + + + + +In the clinic + +The “H-test” +A simple “formula” for remembering the nerves that innervate the extraocular muscles is “LR6SO4 and all the rest are 3” (lateral rectus [VI], superior oblique [IV], all the rest including levator palpebrae superioris are [III]). +The function of all extrinsic muscles and their nerves [III, IV, VI] that move the eyeball in both orbits can all easily be tested at the same time by having the patient track, without moving his or her head, an object such as the tip of a pen or a finger moved in an “H” pattern—starting from the midline between the two eyes (Fig. 8.98). + + + + +2 6 + + + +1 4 +3 5 + + + +Right eye + +1. Lateral rectus [VI] +2. Superior rectus [III] +3. Inferior rectus [III] +4. Medial rectus [III] +5. Superior oblique [IV] +6. Inferior oblique [III] + +Left eye + +Medial rectus [III] +Inferior oblique [III] +Superior oblique [IV] +Lateral rectus [VI] +Inferior rectus [III] +Superior rectus [III] + + +Fig. 8.98 The ���H-test.” + + +930 +Regional Anatomy • Orbit 8 + + + + +Vessels Arteries +The arterial supply to the structures in the orbit, including the eyeball, is by the ophthalmic artery (Fig. 8.99). This vessel is a branch of the internal carotid artery, given off immediately after the internal carotid artery leaves the cavernous sinus. The ophthalmic artery passes into the orbit through the optic canal with the optic nerve. +In the orbit the ophthalmic artery initially lies inferior and lateral to the optic nerve (Fig. 8.99). As it passes forward in the orbit, it crosses superior to the optic nerve and proceeds anteriorly on the medial side of the orbit. +In the orbit the ophthalmic artery gives off numerous branches as follows: + +■ the muscular arteries, which are branches supplying the intrinsic muscles of the eyeball; +■ the supra-orbital artery, which usually arises from the ophthalmic artery immediately after it has crossed the optic nerve, proceeds anteriorly, and exits the orbit through the supra-orbital foramen with the supra-orbital nerve—it supplies the forehead and scalp as it passes across these areas to the vertex of the skull; +■ the posterior ethmoidal artery, which exits the orbit through the posterior ethmoidal foramen to supply the ethmoidal cells and nasal cavity; +■ the anterior ethmoidal artery, which exits the orbit through the anterior ethmoidal foramen, enters the cranial cavity giving off the anterior meningeal branch, and continues into the nasal cavity supplying the septum and lateral wall, and ending as the dorsal nasal artery; + + + +■ the lacrimal artery, which arises from the ophthalmic artery on the lateral side of the optic nerve, and passes anteriorly on the lateral side of the orbit, supplying the lacrimal gland, muscles, the anterior ciliary branch to the eyeball, and the lateral sides of the eyelid; +■ the central retinal artery, which enters the optic nerve, proceeds down the center of the nerve to the retina, and is clearly seen when viewing the retina with an ophthalmoscope—occlusion of this vessel or of the parent artery leads to blindness; + +■ the medial palpebral arteries, which are small branches supplying the medial area of the upper and lower eyelids; +■ the dorsal nasal artery, which is one of the two ter-minal branches of the ophthalmic artery, leaves the orbit to supply the upper surface of the nose; and +■ the supratrochlear artery, which is the other termi-nal branch of the ophthalmic artery and leaves the orbit with the supratrochlear nerve, supplying the forehead as it passes across it in a superior direction. + + + +■ the long and short posterior ciliary arteries, which are branches that enter the eyeball posteriorly, piercing the sclera, and supplying structures inside the eyeball; + +Anterior ethmoidal artery Dorsal nasal artery + + +Veins +There are two venous channels in the orbit, the superior and inferior ophthalmic veins (Fig. 8.100). + + + +Supratrochlear artery Supra-orbital artery +Posterior ethmoidal artery + +Supra-orbital vein +Superior ophthalmic vein + +Cavernous sinus + + + + +Lateral + + +Short posterior ciliary artery +Long posterior ciliary artery +Lacrimal artery + +Central retinal artery + + + + +Ophthalmic artery +Optic nerve + +Fig. 8.99 Arterial supply to the orbit and eyeball. + +Angular vein +Inferior +Inferior ophthalmic vein ophthalmic vein Infra-orbital vein + +Fig. 8.100 Venous drainage of the orbit and eyeball. + + +Pterygoid plexus +of veins + + +931 +Head and Neck + + + +The superior ophthalmic vein begins in the anterior area of the orbit as connecting veins from the supra-orbital vein and the angular vein join together. It passes across the superior part of the orbit, receiving tributaries from the companion veins to the branches of the ophthalmic artery and veins draining the posterior part of the eyeball. Poste-riorly, it leaves the orbit through the superior orbital fissure and enters the cavernous sinus. +The inferior ophthalmic vein is smaller than the superior ophthalmic vein, begins anteriorly, and passes across the inferior part of the orbit. It receives various tributaries from muscles and the posterior part of the eyeball as it crosses the orbit. +The inferior ophthalmic vein leaves the orbit posteriorly by: + + +Lacrimal branch of ophthalmic nerve [V1] Frontal branch of ophthalmic nerve [V1] +Trochlear nerve [IV] +Optic nerve Optic canal +Ophthalmic artery +Superior branch of oculomotor nerve [III] +Nasociliary branch +of ophthalmic nerve [V1] +Abducent nerve [VI] + +Common tendinous ring + +Inferior branch of oculomotor nerve [III] + + + + +■ joining with the superior ophthalmic vein, +■ passing through the superior orbital fissure on its own +to join the cavernous sinus, or Lateral + +Inferior ophthalmic vein + +Superior ophthalmic vein + +Medial + + + +■ passing through the inferior orbital fissure to join with the pterygoid plexus of veins in the infratemporal fossa. + + +Fig. 8.101 Innervation of the orbit and eyeball. + + + +Because the ophthalmic veins communicate with the cavernous sinus, they act as a route by which infections can spread from outside to inside the cranial cavity. + + +Innervation +Numerous nerves pass into the orbit and innervate struc-tures within its bony walls. They include the optic nerve [II], the oculomotor nerve [III], the trochlear nerve [IV], the abducent nerve [VI], and autonomic nerves. Other nerves such as the ophthalmic nerve [V1] innervate orbital structures and then travel out of the orbit to innervate other regions. + + +Superior branch + + + + + + + + +Inferior branch + +Oculomotor nerve [III] + + +Levator palpebrae superioris + +Superior rectus + +Medial rectus +Ciliary ganglion + + + + + +Inferior oblique + + +Inferior rectus + + + +Optic nerve +The optic nerve [II] is not a true cranial nerve, but rather an extension of the brain carrying afferent fibers from the retina of the eyeball to the visual centers of the brain. The optic nerve is surrounded by the cranial meninges, includ-ing the subarachnoid space, which extends as far forward as the eyeball. +Any increase in intracranial pressure therefore results in increased pressure in the subarachnoid space surround-ing the optic nerve. This may impede venous return along the retinal veins, causing edema of the optic disc (papille-dema), which can be seen when the retina is examined using an ophthalmoscope. +The optic nerve leaves the orbit through the optic canal (Fig. 8.101). It is accompanied in the optic canal by the +932 ophthalmic artery. + + +Fig. 8.102 Oculomotor nerve [III] and its divisions. + + +Oculomotor nerve +The oculomotor nerve [III] leaves the anterior surface of the brainstem between the midbrain and the pons. It passes forward in the lateral wall of the cavernous sinus. +Just before entering the orbit the oculomotor nerve [III] divides into superior and inferior branches (Fig. 8.102). These branches enter the orbit through the supe-rior orbital fissure, lying within the common tendinous ring (Fig. 8.101). +Inside the orbit the small superior branch passes upward over the lateral side of the optic nerve to innervate the superior rectus and levator palpebrae superioris muscles (Fig. 8.102). +Regional Anatomy • Orbit 8 + + +The large inferior branch divides into three branches: Superior oblique + + +■ one passing below the optic nerve as it passes to the medial side of the orbit to innervate the medial rectus muscle, +■ a second descending to innervate the inferior rectus muscle, and +■ the third descending as it runs forward along the floor of the orbit to innervate the inferior oblique muscle (Fig. 8.102). + +As the third branch descends, it gives off the branch to + +Medial rectus + +Levator palpebrae superioris + + +Superior rectus + + + +Lateral + + + +the ciliary ganglion. This is the parasympathetic root to the ciliary ganglion and carries preganglionic parasympa-thetic fibers that will synapse in the ciliary ganglion with postganglionic parasympathetic fibers. The postganglionic fibers are distributed to the eyeball through short ciliary nerves and innervate the sphincter pupillae and ciliary muscles. + +Trochlear nerve +The trochlear nerve [IV] arises from the posterior surface Fig. 8.103 Trochlear nerve [IV] in the orbit. of the midbrain, and passes around the midbrain to enter +the edge of the tentorium cerebelli. It continues on an +intradural path arriving in and passing through the lateral + + + +Trochlear nerve [IV] + + + +wall of the cavernous sinus just below the oculomotor nerve [III]. +Just before entering the orbit, the trochlear nerve ascends, passing across the oculomotor nerve [III] and entering the orbit through the superior orbital fissure above the common tendinous ring (Fig. 8.101). In the orbit the trochlear nerve [IV] ascends and turns medially, crossing + +where they synapse with postganglionic sympathetic fibers. +The postganglionic fibers are distributed along the internal carotid artery and its branches. +The postganglionic sympathetic fibers destined for the orbit travel with the ophthalmic artery. Once in the orbit the fibers are distributed to the eyeball either by: + + + +above the levator palpebrae superioris muscle to enter the upper border of the superior oblique muscle (Fig. 8.103). + +Abducent nerve +The abducent nerve [VI] arises from the brainstem between the pons and medulla. It enters the dura covering the clivus and continues in a dural canal until it reaches the cavern-ous sinus. + + +■ passing through the ciliary ganglion, without synaps-ing, and joining the short ciliary nerves, which pass from the ganglion to the eyeball; or +■ passing through long ciliary nerves to reach the eyeball. + +In the eyeball postganglionic sympathetic fibers inner- + +The abducent nerve enters the cavernous sinus and runs through the sinus lateral to the internal carotid artery. It passes out of the sinus and enters the orbit through the superior orbital fissure within the common tendinous ring (Fig. 8.101). Once in the orbit it courses laterally to supply the lateral rectus muscle. + +Postganglionic sympathetic fibers +Preganglionic sympathetic fibers arise from the upper segments of the thoracic spinal cord, mainly T1. They enter the sympathetic chain through white rami commu-nicantes, and ascend to the superior cervical ganglion + +vate the dilator pupillae muscle. + +Ophthalmic nerve [V1] +The ophthalmic nerve [V1] is the smallest and most supe-rior of the three divisions of the trigeminal nerve. This purely sensory nerve receives input from structures in the orbit and from additional branches on the face and scalp. +Leaving the trigeminal ganglion, the ophthalmic nerve [V1] passes forward in the lateral wall of the cavernous sinus inferior to the trochlear [IV] and oculomotor [III] nerves. Just before it enters the orbit it divides into three +branches—the nasociliary, lacrimal, and frontal nerves 933 +Head and Neck + + + +Anterior ethmoidal nerve Infratrochlear nerve +Supratrochlear nerve +Supra-orbital nerve Posterior ethmoidal nerve + + +Lateral + + +Lacrimal nerve (from [V1]) Long ciliary nerves +Frontal nerve (from [V1]) Nasociliary nerve (from [V1]) +Optic nerve [II] +Ophthalmic nerve [V1] + +Fig. 8.104 Ophthalmic nerve [V1] and its divisions. + + +(Fig. 8.104). These branches enter the orbit through the superior orbital fissure with the frontal and lacrimal nerves outside the common tendinous ring, and the nasociliary nerve within the common tendinous ring (Fig. 8.101). + +Lacrimal nerve +The lacrimal nerve is the smallest of the three branches of + +Superior oblique +Supratrochlear nerve + +Supra-orbital nerve + +Levator palpebrae superioris + +Superior rectus +Lacrimal gland + + +Medial rectus Lateral rectus +Lacrimal nerve (from [V1]) Frontal nerve (from [V1]) Nasociliary nerve (from [V1]) + +Trochlear nerve [IV] + +Ophthalmic nerve [V1] + + +Lateral + + + + + +Fig. 8.105 Relationship of the ophthalmic nerve [V1] and its divisions to the muscles of the eyeball. + + + +the ophthalmic nerve [V1]. Once in the orbit it passes forward along the upper border of the lateral rectus muscle (Fig. 8.105). It receives a branch from the zygomaticotem-poral nerve, which carries parasympathetic and sympa-thetic postganglionic fibers for distribution to the lacrimal gland. +Reaching the anterolateral aspect of the orbit, the lac-rimal nerve supplies the lacrimal gland, conjunctiva, and lateral part of the upper eyelid. + +Frontal nerve +The frontal nerve is the largest branch of the ophthalmic nerve [V1] and receives sensory input from areas outside the orbit. Exiting the superior orbital fissure, this branch + + +exits the orbit medial to the supra-orbital foramen, and supplies the conjunctiva and skin of the upper eyelid and the skin on the lower medial part of the forehead. +■ The supra-orbital nerve is the larger of the two branches, continues forward, passing between the levator palpebrae superioris muscle and the periorbita covering the roof of the orbit (Fig. 8.105), exits the orbit through the supra-orbital notch and ascends across the forehead and scalp, supplying the upper eyelid and conjunctiva, the forehead, and as far posteriorly as the middle of the scalp. + + + +passes forward between the levator palpebrae superioris and the periorbita on the roof of the orbit (Fig. 8.101). About midway across the orbit it divides into its two termi-nal branches—the supra-orbital and supratrochlear nerves (Figs. 8.104 and 8.105): + + +Nasociliary nerve +The nasociliary nerve is intermediate in size between the frontal and lacrimal nerves and is usually the first branch from the ophthalmic nerve (Fig. 8.104). It is most deeply placed in the orbit, entering the area within the common + + + +■ The supratrochlear nerve continues forward in an 934 anteromedial direction, passing above the trochlea, + +tendinous ring between the superior and inferior branches of the oculomotor nerve [III] (see Fig. 8.101). +Regional Anatomy • Orbit 8 + + + +Once in the orbit, the nasociliary nerve crosses the superior surface of the optic nerve as it passes in a medial direction below the superior rectus muscle (Figs. 8.104 and 8.106). Its first branch, the communicating branch with the ciliary ganglion (sensory root to the ciliary ganglion), is given off early in its path through the orbit. The nasociliary nerve continues forward along the medial wall of the orbit, between the superior oblique and the medial rectus muscles, giving off several branches (Fig. +8.106). These include: + +anterior cranial fossa, nasal cavity, and skin of the lower half of the nose (Fig. 8.106). + +Ciliary ganglion +The ciliary ganglion is a parasympathetic ganglion of the oculomotor nerve [III]. It is associated with the naso-ciliary branch of the ophthalmic nerve [V1] and is the site where preganglionic and postganglionic parasympathetic neurons synapse as fibers from this part of the autonomic division of the PNS make their way to the eyeball. The + + + + +■ the long ciliary nerves, which are sensory to the eyeball but may also contain sympathetic fibers for pupillary dilation; +■ the posterior ethmoidal nerve, which exits the orbit through the posterior ethmoidal foramen to supply posterior ethmoidal cells and the sphenoidal sinus; +■ the infratrochlear nerve, which distributes to the medial part of the upper and lower eyelids, the lacrimal sac, and skin of the upper half of the nose; and +■ the anterior ethmoidal nerve, which exits the orbit through the anterior ethmoidal foramen to supply the + +ciliary ganglion is also traversed by postganglionic sympa-thetic fibers and sensory fibers as they travel to the eyeball. The ciliary ganglion is a very small ganglion, in the posterior part of the orbit immediately lateral to the optic nerve and between the optic nerve and the lateral rectus muscle (Fig. 8.106). It is usually described as receiving at least two, and possibly three, branches or roots from other +nerves in the orbit. + +Parasympathetic root +As the inferior branch of the oculomotor nerve [III] passes the area of the ciliary ganglion, it sends a branch to the ganglion (the parasympathetic root). The parasympathetic + +Posterior ethmoidal nerve branch carries preganglionic parasympathetic fibers, + +Anterior ethmoidal nerve + +Infratrochlear nerve + +Medial rectus muscle +Long ciliary nerves Short ciliary nerves +Lacrimal gland + +which enter the ganglion and synapse with postganglionic parasympathetic fibers within the ganglion (Fig. 8.107). +The postganglionic parasympathetic fibers leave the ganglion through short ciliary nerves, which enter the posterior aspect of the eyeball around the optic nerve. +In the eyeball the parasympathetic fibers innervate: + + + + +Lateral + +Lacrimal nerve (from [V1]) +Lateral rectus + +■ the sphincter pupillae muscle, responsible for pupil-lary constriction, and +■ the ciliary muscle, responsible for accommodation of the lens of the eye for near vision. + + + +Ciliary ganglion + +Abducent nerve [VI] + +Inferior branch of the oculomotor nerve [III] + + +Sensory root +Nasociliary nerve +Long ciliary nerve + +Sympathetic root + + + +Nasociliary nerve (from [V1]) + + +Parasympathetic (motor) root + + + +Ciliary ganglion + + + +Superior branch of the oculomotor nerve [III] + + + +Fig. 8.106 Course of the nasociliary nerve (from [V1]) in the orbit. + + +Oculomotor nerve [III] Short ciliary nerve + +Sensory fibers +Sympathetic postganglionic fibers Parasympathetic preganglionic fibers Parasympathetic postganglionic fibers + +Fig. 8.107 Ciliary ganglion. 935 +Head and Neck + + + +Sensory root +A second branch (the sensory root), passes from the naso-ciliary nerve to the ganglion (Fig. 8.107). This branch enters the posterosuperior aspect of the ganglion, and carries sensory fibers, which pass through the ganglion and continue along the short ciliary nerves to the eyeball. These fibers are responsible for sensory innervation to all parts of the eyeball; however, the sympathetic fibers also may take alternative routes to the eyeball. + +Sympathetic root +The third branch to the ciliary ganglion is the most vari-able. This branch, when present, is the sympathetic root and contains postganglionic sympathetic fibers from the superior cervical ganglion (Fig. 8.107). These fibers travel up the internal carotid artery, leave the plexus surround-ing the artery in the cavernous sinus, and enter the orbit through the common tendinous ring. In the orbit they enter the posterior aspect of the ciliary ganglion, cross the ganglion, and continue along the short ciliary nerves to the eyeball; however, the sympathetic fibers also may take alternative routes to the eyeball. +Sympathetic fibers to the eyeball may not enter the gan-glion as a separate sympathetic root. Rather, the postgan-glionic sympathetic fibers may leave the plexus associated + + + +Long posterior ciliary artery + + + +Short posterior ciliary arteries + +Optic nerve + +Optic disc + + + +Fovea centralis + + +with the internal carotid artery in the cavernous sinus, join the ophthalmic nerve [V1], and course into the ciliary ganglion in the sensory root from the nasociliary nerve. In addition, the sympathetic fibers carried in the nasociliary nerve may not enter the ganglion at all and may course directly into the eyeball in the long ciliary nerves (Fig. 8.107). Whatever their path, postganglionic sympathetic fibers reach the eyeball and innervate the dilator pupillae muscle. + +Eyeball +The globe-shaped eyeball occupies the anterior part of the orbit. Its rounded shape is disrupted anteriorly, where it bulges outward. This outward projection represents about one-sixth of the total area of the eyeball and is the trans-parent cornea (Fig. 8.108). +Posterior to the cornea and in order from front to back are the anterior chamber, the iris and pupil, the posterior chamber, the lens, the postremal (vitreous) chamber, and the retina. + +Anterior and posterior chambers +The anterior chamber is the area directly posterior to the cornea and anterior to the colored part of the eye (iris). The central opening in the iris is the pupil. Posterior to the + + +Postremal (vitreous) chamber + +Ora serrata + + + +Posterior chamber + +Anterior chamber + +Cornea + + +Lens + + +Iris + + + +Scleral venous sinus + +Ciliary body +Sclera +Choroid +Retina + +Anterior ciliary artery + +936 Fig. 8.108 Eyeball. +Regional Anatomy • Orbit 8 + + +iris and anterior to the lens is the smaller posterior chamber. +The anterior and posterior chambers are continuous + +Vessels Arterial supply +The arterial supply to the eyeball is from several sources: + + + +with each other through the pupillary opening. They are filled with a fluid (aqueous humor), which is secreted into the posterior chamber, flows into the anterior chamber through the pupil, and is absorbed into the scleral venous sinus (the canal of Schlemm), which is a circular venous channel at the junction between the cornea and the iris (Fig. 8.108). +The aqueous humor supplies nutrients to the avascular cornea and lens and maintains the intra-ocular pressure. If the normal cycle of its production and absorption is disturbed so that the amount of fluid increases, intra-ocular pressure will increase. This condition (glaucoma) can lead to a variety of visual problems. + +Lens and vitreous humor + + +■ The short posterior ciliary arteries are branches from the ophthalmic artery that pierce the sclera around the optic nerve and enter the choroid layer (Fig. 8.108). +■ The long posterior ciliary arteries, usually two, enter the sclera on the medial and lateral sides of the optic nerve and proceed anteriorly in the choroid layer to anasto-mose with the anterior ciliary arteries. +■ The anterior ciliary arteries are branches of the arteries supplying the muscles (Fig. 8.108)—as the muscles attach to the sclera, these arteries pierce the sclera to anastomose with the long posterior ciliary arteries in the choroid layer. +■ The central retinal artery that has traversed the optic nerve and enters the area of the retina at the optic disc. + + + +The lens separates the anterior one-fifth of the eyeball from the posterior four-fifths (Fig. 8.108). It is a transpar-ent, biconvex elastic disc attached circumferentially to muscles associated with the outer wall of the eyeball. This lateral attachment provides the lens with the ability to change its refractive ability to maintain visual acuity. The clinical term for opacity of the lens is a cataract. +The posterior four-fifths of the eyeball, from the lens to the retina, is occupied by the postremal (vitreous) chamber (Fig. 8.108). This segment is filled with a transparent, gelatinous substance—the vitreous body (vitreous humor). This substance, unlike aqueous humor, cannot be replaced. + +Walls of the eyeball +Surrounding the internal components of the eyeball are the walls of the eyeball. They consist of three layers: an outer fibrous layer, a middle vascular layer, and an inner retinal layer (Fig. 8.108). + + +Venous drainage +Venous drainage of the eyeball is primarily related to drain-age of the choroid layer. Four large veins (the vorticose veins) are involved in this process. They exit through the sclera from each of the posterior quadrants of the eyeball and enter the superior and inferior ophthalmic veins. There is also a central retinal vein accompanying the central retinal artery. + +In the clinic + +Glaucoma +Intraocular pressure will rise if the normal cycle of aqueous humor fluid production and absorption is disturbed so that the amount of fluid increases. This condition is glaucoma and can lead to a variety of visual problems including blindness, which results from compression of the retina and its blood supply. + + + +■ The outer fibrous layer consists of the sclera posteriorly and the cornea anteriorly. +■ The middle vascular layer consists of the choroid pos-teriorly and is continuous with the ciliary body and iris anteriorly. +■ The inner layer consists of the optic part of the retina posteriorly and the nonvisual retina that covers the internal surface of the ciliary body and iris anteriorly. + + +In the clinic + +Cataracts +With increasing age and in certain disease states the lens of the eye becomes opaque. Increasing opacity results in increasing visual impairment. A common operation is excision of the cloudy lens and replacement with a new man-made lens. + + + + + + + +937 +Head and Neck + + + +In the clinic + +Ophthalmoscopy +Direct visualization of the postremal (vitreous) chamber of the eye is possible in most clinical settings. It is achieved using an ophthalmoscope, which is a small battery-operated light with a tiny lens that allows direct visualization of the postremal (vitreous) chamber and the posterior wall of the eye through the pupil and the lens. It is sometimes + + + +necessary to place a drug directly onto the eye to dilate the pupil for better visualization. +The optic nerve, observed as the optic disc, is easily seen. The typical four branches of the central retinal artery and the fovea are also seen. +Using ophthalmoscopy the physician can look for diseases of the optic nerve, vascular abnormalities, and changes within the retina (Fig. 8.109). + + +Superior temporal retinal arteriole and venule + + + + + +Superior nasal retinal arteriole and venule + +Central retinal artery + + +Nasal + +Optic disc + +Central retinal vein + + +Superior and inferior macular arteriole and venule + + +Temporal + +Macula lutea with fovea centralis + + + + + + + +Inferior temporal retinal arteriole and venule Inferior nasal retinal arteriole and venule + +Fig. 8.109 Ophthalmoscopic view of posterior chamber of the right eye. + + + + +Fibrous layer of the eyeball +The fibrous layer of the eyeball consists of two components— the sclera covers the posterior and lateral parts of the eyeball, about five-sixths of the surface, and the cornea covers the anterior part (Fig. 8.108). + +Sclera +The sclera is an opaque layer of dense connective tissue that can be seen anteriorly through its conjunctival cover-ing as the “white of the eye.” It is pierced by numerous vessels and nerves, including the optic nerve posteriorly and provides attachment for the various muscles involved +938 in eyeball movements. + + +The fascial sheath of the eyeball covers the surface of the sclera externally from the entrance of the optic nerve to the corneoscleral junction while internally the surface of the sclera is loosely attached to the choroid of the vas-cular layer. + +Cornea +Continuous with the sclera anteriorly is the transparent cornea. It covers the anterior one-sixth of the surface of the eyeball and, being transparent, allows light to enter the eyeball. +Regional Anatomy • Orbit 8 + + + +Vascular layer of the eyeball +The vascular layer of the eyeball consists of three continu-ous parts—the choroid, the ciliary body, and the iris from posterior to anterior (Fig. 8.108). + +Choroid +The choroid is posterior and represents approximately two- + + +Iris +Completing the vascular layer of the eyeball anteriorly is the iris (Fig. 8.108). This circular structure, projecting outward from the ciliary body, is the colored part of the eye with a central opening (the pupil). Controlling the size of the pupil are smooth muscle fibers (sphincter pupillae) and myoepithe-lial cells (dilator pupillae) within the iris (Fig. 8.110): + + + +thirds of the vascular layer. It is a thin, highly vascular, pigmented layer consisting of smaller vessels adjacent to the retina and larger vessels more peripherally. It is firmly attached to the retina internally and loosely attached to the sclera externally. + + +■ Fibers arranged in a circular pattern make up the sphincter pupillae muscle (Table 8.9), which is innervated by parasympathetics—contraction of its fibers decreases or constricts the pupillary opening. + + + +Ciliary body +Extending from the anterior border of the choroid is the ciliary body (Fig. 8.108). This triangular-shaped structure, between the choroid and the iris, forms a complete ring around the eyeball. Its components include the ciliary muscle and the ciliary processes (Fig. 8.110). +The ciliary muscle consists of smooth muscle fibers arranged longitudinally, circularly, and radially. Controlled by parasympathetics traveling to the orbit + + + + +Sclera +Choroid + + + + + + + +Ciliary muscle + +Ciliary process + + + + + + + + + +Ciliary body + + + +in the oculomotor nerve [III], these muscle fibers, on contraction, decrease the size of the ring formed by the ciliary body. +The ciliary processes are longitudinal ridges project-ing from the inner surface of the ciliary body (Fig. 8.110). Extending from them are zonular fibers attached to the lens of the eyeball, which suspend the lens in its proper position and collectively form the suspensory ligament of the lens. +Contraction of the ciliary muscle decreases the size of the ring formed by the ciliary body. This reduces tension on the suspensory ligament of the lens. The lens therefore becomes more rounded (relaxed) resulting in accommoda-tion of the lens for near vision. + + +Posterior chamber Scleral venous sinus +Dilator pupillae + +Iris + +Sphincter pupillae + + + +Cornea + + + +Lens Zonular fibers Anterior chamber + + + +Ciliary processes also contribute to the formation of aqueous humor. + + +Fig. 8.110 Ciliary body. + + + + + + + +Table 8.9 + +Muscle +Ciliary + +Intrinsic muscles of the eye + +Location +Muscle fibers in the ciliary body + + + +Innervation +Parasympathetics from the oculomotor nerve [III] + + + +Function +Constricts ciliary body, relaxes tension on lens, lens becomes more rounded + + + +Sphincter pupillae + +Dilator pupillae + +Circularly arranged fibers in the iris + +Radially arranged fibers in the iris + +Parasympathetics from the oculomotor nerve [III] +Sympathetics from the superior cervical ganglion (T1) + +Constricts pupil + +Dilates pupil + +939 +Head and Neck + + + +■ Contractile fibers arranged in a radial pattern make up the dilator pupillae muscle, which is innervated by sympathetics—contraction of its fibers increases or dilates the pupillary opening. + +pigmented layer around the optic nerve and at the ora serrata. + +It is the neural layer that separates in the case of a detached retina. + + +Inner layer of the eyeball +The inner layer of the eyeball is the retina (Fig. 8.108). It consists of two parts. Posteriorly and laterally is the optic part of the retina, which is sensitive to light, and anteri-orly is the nonvisual part, which covers the internal surface of the ciliary body and the iris. The junction between these parts is an irregular line (the ora serrata). + +Optic part of the retina +The optic part of the retina consists of two layers, an outer pigmented layer and an inner neural layer: + +Several obvious features are visible on the posterior surface of the optic part of the retina. +The optic disc is where the optic nerve leaves the retina (Fig. 8.109). It is lighter than the surrounding retina and branches of the central retinal artery spread from this point outward to supply the retina. As there are no light-sensitive receptor cells in the optic disc, it is referred to as a blind spot in the retina. +Lateral to the optic disc a small area with a hint of yel-lowish coloration is the macula lutea with its central depression, the fovea centralis (Fig. 8.109). This is the thinnest area of the retina and visual sensitivity here is higher than elsewhere in the retina because it has fewer + + + +■ The pigmented layer is firmly attached to the choroid and continues anteriorly over the internal surface of the ciliary body and iris. +■ The neural layer, which can be further subdivided into its various neural components, is only attached to the + +rods (light-sensitive receptor cells that function in dim light and are insensitive to color) and more cones (light-sensitive receptor cells that respond to bright light and are sensitive to color). + + + + + + + + + +In the clinic + +High-definition optical coherence tomography +High-definition optical coherence tomography (HD-OCT) (Fig. 8.111) is a procedure used to obtain subsurface images of translucent or opaque materials. It is similar to ultrasound, except that it uses light instead of sound to produce +high-resolution cross-sectional images. It is especially useful in the diagnosis and management of optic nerve and retinal diseases. + + + +Epiretinal membrane +An epiretinal membrane (Fig. 8.112) is a thin sheet of fibrous tissue that develops on the surface of the retina in the area of the macula and can cause visual problems. If the visual problems are significant, surgical removal of the membrane may be necessary. + + + + + + + + + + + + + + + +940 +Regional Anatomy • Orbit 8 + + +In the clinic—cont’d + +1 +11 3 4 5 6 9A 9B 10 7 8 1 2 2 3 + +4 + + +5 + +6 + + +7 + + +A + +1 2 3 4 5 6 7 8 9A 9B 10 11 + + +Fovea + + + +B + + +8 +A 9 B + +10 + +11 + +C + + + +1 Internal limiting membrane 2 Nerve fiber layer +3 Ganglion cell layer + +4 Inner plexiform layer 5 Inner nuclear layer +6 Outer plexiform layer + +7 Outer nuclear layer +8 External limiting membrane +9A Photoreceptor inner layer + +9B Photoreceptor outer layer 10 Pigment epithelium +11 Choroid + + +Fig. 8.111 Layers of the retina in a healthy eye. A. HD-OCT scan of a healthy eye. B. Schematic indicating the layers of the retina on an HD-OCT scan of a healthy eye. C. Diagram illustrating the layers of the retina. + +Optic disc Optic disc + + + + + +Epiretinal Fovea membrane + + + + + + + + + + + + + +A Left eye B Right eye + +Fig. 8.112 High-definition optical coherence tomography (HD-OCT). A. Diseased eye. B. Healthy eye. +941 +Head and Neck + + + +EAR + +The ear is the organ of hearing and balance. It has three parts (Fig. 8.113): + +■ The third part is the internal ear consisting of a series of cavities within the petrous part of the temporal bone between the middle ear laterally and the internal acous-tic meatus medially. + + + +■ The first part is the external ear consisting of the part attached to the lateral aspect of the head and the canal leading inward. +■ The second part is the middle ear—a cavity in the petrous part of the temporal bone bounded laterally, and separated from the external canal, by a mem-brane and connected internally to the pharynx by a narrow tube. + + +The internal ear converts the mechanical signals received from the middle ear, which start as sound captured by the external ear, into electrical signals to transfer infor-mation to the brain. The internal ear also contains recep-tors that detect motion and position. + + + + + + + +External ear Middle ear Internal ear + + + + + + + + + + + + +Internal acoustic meatus + +Auricle + + + +External acoustic meatus + + + +Cartilage + + + +Tympanic membrane + + +Pharynx + + +Pharyngotympanic tube + + + + +Fig. 8.113 Right ear. + + + + + + + +942 +Regional Anatomy • Ear 8 + + + +External ear +The external ear consists of two parts. The part projecting from the side of the head is the auricle (pinna) and the + + +Muscles +Numerous intrinsic and extrinsic muscles are associated with the auricle: + + + +canal leading inward is the external acoustic meatus. + +Auricle +The auricle is on the side of the head and assists in captur-ing sound. It consists of cartilage covered with skin and arranged in a pattern of various elevations and depressions (Fig. 8.114). +The large outside rim of the auricle is the helix. It ends inferiorly at the fleshy lobule, the only part of the auricle not supported by cartilage. + + +■ The intrinsic muscles pass between the cartilaginous parts of the auricle and may change the shape of the auricle. +■ The extrinsic muscles, the anterior, superior, and poste-rior auricular muscles, pass from the scalp or skull to the auricle and may also play a role in positioning of the auricle (see Fig. 8.56). + +Both groups of muscles are innervated by the facial + + + +The hollow center of the auricle is the concha of the auricle. The external acoustic meatus leaves from the depths of this area. +Just anterior to the opening of the external acoustic meatus, in front of the concha, is an elevation (the tragus). Opposite the tragus, and above the fleshy lobule, is another + +nerve [VII]. + +Innervation +Sensory innervation of the auricle is from many sources (Fig. 8.115): + + + +elevation (the antitragus). A smaller curved rim, parallel and anterior to the helix, is the antihelix. + +■ The outer more superficial surfaces of the auricle are supplied by the great auricular nerve (anterior and + + + + + + + + + + + + + + +Helix + + +Antihelix + + + + +Concha Lesser occipital nerve (C2) + + +Tragus + +Auriculotemporal branch of the mandibular nerve [V3] + + +External acoustic meatus + + + + +Vagus nerve [X] +Antitragus Lobule Facial nerve [VII] + +Great auricular nerve (C2,C3) + + +Fig. 8.114 Auricle. Fig. 8.115 Sensory innervation of the auricle. + + + + + +943 +Head and Neck + + + +posterior inferior portions) and the lesser occipital nerve (posterosuperior portion) from the cervical plexus and the auriculotemporal branch of the mandibular nerve [V3] (anterosuperior portion). +■ The deeper parts of the auricle are supplied by the vagus nerve [X] (the auricular branch) and the facial nerve [VII] (which sends a branch to the auricular branch of the vagus nerve [X]). + + +External acoustic meatus +The external acoustic meatus extends from the deepest part of the concha to the tympanic membrane (eardrum), a distance of approximately 1 inch (2.5 cm) (Fig. 8.116). Its walls consist of cartilage and bone. The lateral one-third is formed from cartilaginous extensions from some of the auricular cartilages and the medial two-thirds is a bony tunnel in the temporal bone. + + +Vessels +The arterial supply to the auricle is from numerous sources. The external carotid artery supplies the posterior auricular artery, the superficial temporal artery supplies anterior auricular branches, and the occipital artery supplies a branch. + +Throughout its length the external acoustic meatus is covered with skin, some of which contains hair and modi-fied sweat glands producing cerumen (earwax). Its diam-eter varies, being wider laterally and narrow medially. +The external acoustic meatus does not follow a straight course. From the external opening it passes upward in an anterior direction, then turns slightly posteriorly still + + + +Venous drainage is through vessels following the arteries. + +passing upward, and finally, turns again in an anterior direction with a slight descent. For examination purposes, + + + +Lymphatic drainage of the auricle passes anteriorly into parotid nodes and posteriorly into mastoid nodes, and pos-sibly into the upper deep cervical nodes. + +observation of the external acoustic meatus and tympanic membrane can be improved by pulling the ear superiorly, posteriorly, and slightly laterally. + + + + + + + + + + + +External acoustic meatus + + +Tympanic membrane + + + + + + + + + + + + +Auricle Cartilage Bone + + + + + + +944 Fig. 8.116 External acoustic meatus. +Regional Anatomy • Ear 8 + + +Innervation Malleus Middle ear Sensory innervation of the external acoustic meatus is +from several of the cranial nerves. The major sensory input travels through branches of the auriculotemporal nerve, a branch of the mandibular nerve [V3] (anterior and superior walls), and in the auricular branch of the vagus nerve [X] (posterior and inferior walls). A minor sensory input may also come from a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X]. + +Tympanic membrane +The tympanic membrane separates the external acoustic meatus from the middle ear (Figs. 8.117 and 8.118). It is at an angle, sloping medially from top to bottom and pos-teriorly to anteriorly. Its lateral surface therefore faces + +inferiorly and anteriorly. It consists of a connective tissue core lined with skin on the outside and mucous membrane on the inside. +Around the periphery of the tympanic membrane a fibrocartilaginous ring attaches it to the tympanic part of the temporal bone. At its center, a concavity is produced + + +External acoustic meatus + +Tympanic membrane + + +Fig. 8.117 Middle ear. + + + + +Pharyngotympanic tube + + + + + + + + +Pars flaccida + +Posterior malleolar fold + + +Lateral process (of malleus) + + + +Anterior malleolar fold + +Handle of malleus + + + + +Umbo Cone of light B A + +Fig. 8.118 Tympanic membrane (right ear). A. Diagram. B. Otoscopic view. + + + + + + + + +945 +Head and Neck + + + +by the attachment on its internal surface of the lower end of the handle of the malleus, part of the malleus bone in the middle ear. This point of attachment is the umbo of the tympanic membrane. +Anteroinferior to the umbo of the tympanic membrane a bright reflection of light, referred to as the cone of light, is usually visible when examining the tympanic membrane with an otoscope. +Superior to the umbo in an anterior direction is the attachment of the rest of the handle of the malleus (Fig. 8.118). At the most superior extent of this line of attach-ment a small bulge in the membrane marks the position of the lateral process of the malleus as it projects against the internal surface of the tympanic membrane. Extending away from this elevation, on the internal surface of the membrane, are the anterior and posterior malleolar folds. Superior to these folds the tympanic membrane is thin and slack (the pars flaccida), whereas the rest of the membrane is thick and taut (the pars tensa). + +Innervation +Innervation of the external and internal surfaces of the tympanic membrane is by several cranial nerves: + +■ Sensory innervation of the skin on the outer surface of the tympanic membrane is primarily by the auriculo-temporal nerve, a branch of the mandibular nerve [V3] with additional participation of the auricular branch of the vagus nerve [X], a small contribution by a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X], and possibly a contribution from the glossopharyngeal nerve [IX]. +■ Sensory innervation of the mucous membrane on the inner surface of the tympanic membrane is carried entirely by the glossopharyngeal [IX] nerve. + + +In the clinic + +Otitis media +The eustachian tube links the middle ear and pharynx and balances the pressure between the outer and middle ear. Colds and allergies, particularly in children, can result in swelling of the lining of the eustachian tube, which can then impair normal drainage of fluid from the middle ear. The fluid then builds up behind the tympanic membrane, providing an attractive environment for bacteria and viruses to grow and cause otitis media. Left untreated, otitis media can lead to perforation of the tympanic membrane, hearing loss, meningitis, and brain abscess. + + + +In the clinic + +Examination of the ear +The ear comprises three components—the external, middle, and internal ear. +Clinical examination is carried out to assess hearing and balance. Further examination involves use of an otoscope or other imaging techniques. +External ear +The external ear is easily examined. The external acoustic meatus and the tympanic membrane require otoscopic examination (Fig. 8.118B). An otoscope is a device through which light can be shone and the image magnified to inspect the external acoustic meatus and the tympanic membrane. +The examination begins by grasping the posterosuperior aspect of the ear and gently retracting it to straighten the external auditory meatus. The normal tympanic membrane is relatively translucent and has a gray–reddish tinge. The handle of the malleus is visible near the center of the membrane. In the 5 o’clock position a cone of light is always demonstrated. +Middle and inner ears +The middle ear is investigated by CT and MRI to visualize the malleus, incus, and stapes. The relationship of these bones to the middle ear cavity is determined and any masses identified. +The inner ear is also assessed by CT and MRI. + + + + + + + + + + + + +946 +Regional Anatomy • Ear 8 + + +In the clinic Epitympanic recess + +Swimmer’s ear +Swimmer’s ear, often called otitis externa, is a painful condition resulting from an infection in the external acoustic meatus. It frequently occurs in swimmers. + + +External acoustic meatus + + +Malleus + +Incus + +Oval window + +Stapes Internal ear + + + + + +In the clinic + +Surfer’s ear +Surfer’s ear, which is prevalent among individuals who surf or swim in cold water, results from the development of a “bony lump” in the external acoustic meatus. Growth of the lump eventually constricts the meatus and reduces hearing in the affected ear. + + + + + +In the clinic + +Tympanic membrane perforation +Although perforation of the tympanic membrane (eardrum) has many causes, trauma and infection are the most common. +Ruptures of the tympanic membrane tend to heal spontaneously, but surgical intervention may be necessary if the rupture is large. +Occasionally, it may be necessary to enter the middle ear through the tympanic membrane. Because the chorda tympani runs in the upper one-third of the tympanic membrane, incisions are always below this level. The richer blood supply to the posterior aspect of the tympanic membrane determines the standard surgical approach in the posteroinferior aspect. +Otitis media (infection of the middle ear) is common and can lead to perforation of the tympanic membrane. The infection can usually be treated with antibiotics. If the infection persists, the chronic inflammatory change may damage the ossicular chain and other structures within the middle ear to produce deafness. + + + +Middle ear +The middle ear is an air-filled, mucous membrane–lined space in the temporal bone between the tympanic mem-brane laterally and the lateral wall of the internal ear medi-ally. It is described as consisting of two parts (Fig. 8.119): + + + + + + + + + +Tympanic membrane Pharyngotympanic tube + +Fig. 8.119 Parts of the middle ear. + + + +■ the tympanic cavity immediately adjacent to the tympanic membrane, and +■ the epitympanic recess superiorly. + + +The middle ear communicates with the mastoid area posteriorly and the nasopharynx (via the pharyngotym-panic tube) anteriorly. Its basic function is to transmit vibrations of the tympanic membrane across the cavity of the middle ear to the internal ear. It accomplishes this through three interconnected but movable bones that bridge the space between the tympanic membrane and the internal ear. These bones are the malleus (connected to the tympanic membrane), the incus (connected to the malleus by a synovial joint), and the stapes (connected to the incus by a synovial joint, and attached to the lateral wall of the internal ear at the oval window). + + + +947 +Head and Neck + + + + +Boundaries +The middle ear has a roof and a floor, and anterior, poste-rior, medial, and lateral walls (Fig. 8.120). + +Tegmental wall +The tegmental wall (roof) of the middle ear consists of a thin layer of bone, which separates the middle ear from the middle cranial fossa. This layer of bone is the tegmen tympani on the anterior surface of the petrous part of the temporal bone. + +Jugular wall +The jugular wall (floor) of the middle ear consists of a thin layer of bone that separates it from the internal jugular + +vein. Occasionally, the floor is thickened by the presence of mastoid air cells. +Near the medial border of the floor is a small aperture, through which the tympanic branch from the glossopha-ryngeal nerve [IX] enters the middle ear. + +Membranous wall +The membranous (lateral) wall of the middle ear consists almost entirely of the tympanic membrane, but because the tympanic membrane does not extend superiorly into the epitympanic recess, the upper part of the membranous wall of the middle ear is the bony lateral wall of the epi-tympanic recess. + + + + + + + + + +Prominence of lateral semicircular canal Prominence of facial canal Tegmen tympani +Promontory + + +Tensor tympani muscle + + +Aditus to +mastoid antrum Pharyngotympanic tube + + + +Oval window + + +Pyramidal eminence Lesser petrosal nerve +Branch from internal carotid plexus + + +Chorda tympani nerve +Sympathetic plexus + + + + +Round window + + + +Facial nerve [VII] + +Internal carotid artery + +Chorda tympani nerve + +Tympanic branch of the glossopharyngeal nerve [IX] + +Internal jugular vein + + + +948 Fig. 8.120 Boundaries of the right middle ear. +Regional Anatomy • Ear 8 + + + + +Mastoid wall +The mastoid (posterior) wall of the middle ear is only par-tially complete. The lower part of this wall consists of a bony partition between the tympanic cavity and mastoid air cells. Superiorly, the epitympanic recess is continuous with the aditus to the mastoid antrum (Figs. 8.120 and 8.121). + +Associated with the mastoid wall are: + +■ the pyramidal eminence, a small elevation through which the tendon of the stapedius muscle enters the middle ear; and +■ the opening through which the chorda tympani nerve, a branch of the facial nerve [VII], enters the middle ear. + + + + + + + +Mastoid antrum Aditus to mastoid antrum + +Tegmen tympani +Epitympanic recess + +Anterior wall +The anterior wall of the middle ear is only partially com-plete. The lower part consists of a thin layer of bone that separates the tympanic cavity from the internal carotid artery. Superiorly, the wall is deficient because of the presence of: + +■ a large opening for the entrance of the pharyngotym-panic tube into the middle ear, and +■ a smaller opening for the canal containing the tensor tympani muscle. + +The foramen for the exit of the chorda tympani + +Pharyngotympanic tube + +Middle ear A Mastoid process + +Mastoid air cells + +nerve from the middle ear is also associated with this wall (Fig. 8.120). + +Labyrinthine wall +The labyrinthine (medial) wall of the middle ear is also the + + + + +Cochlea Middle ear External auditory meatus + +lateral wall of the internal ear. A prominent structure on this wall is a rounded bulge (the promontory) produced by the basal coil of the cochlea, which is an internal ear structure involved with hearing (Fig. 8.120). +Associated with the mucous membrane covering the promontory is a plexus of nerves (the tympanic plexus), which consists primarily of contributions from the tym-panic branch of the glossopharyngeal nerve [IX] and branches from the internal carotid plexus. It supplies the mucous membrane of the middle ear, the mastoid area, and the pharyngotympanic tube. +Additionally, a branch of the tympanic plexus (the lesser petrosal nerve) leaves the promontory and the middle ear, travels across the anterior surface of the petrous part of the temporal bone, and leaves the middle cranial fossa through the foramen ovale to enter the otic ganglion. Other struc-tures associated with the labyrinthine wall are two open-ings, the oval and round windows, and two prominent elevations (Fig. 8.120): + + + +B + +Mastoid air cells + + +■ The oval window is posterosuperior to the promontory, is the point of attachment for the base of the stapes (footplate), and ends the chain of bones that transfer + +Fig. 8.121 Mastoid antrum and surrounding bone. A. Diagram. B. High-resolution CT scan of left ear (petrous temporal bone). + + +vibrations initiated by the tympanic membrane to the cochlea of the internal ear. 949 +Head and Neck + + +■ The round window is posteroinferior to the External acoustic meatus promontory. Malleus Stapes + +■ Posterior and superior to the oval window on the medial wall is the prominence of the facial canal, which is a ridge of bone produced by the facial nerve [VII] in its canal as it passes through the temporal bone. +■ Just above and posterior to the prominence of the facial canal is a broader ridge of bone (prominence of the lateral semicircular canal) produced by the lateral semicircular canal, which is a structure involved in detecting motion. + + +Incus Middle ear + +Internal ear + + + +Mastoid area +Posterior to the epitympanic recess of the middle ear is the aditus to the mastoid antrum, which is the opening to the mastoid antrum (Fig. 8.121). +The mastoid antrum is a cavity continuous with col-lections of air-filled spaces (the mastoid cells), throughout the mastoid part of the temporal bone, including the mastoid process. The mastoid antrum is separated from the middle cranial fossa above by only the thin tegmen tympani. The mucous membrane lining the mastoid air cells is continuous with the mucous membrane throughout the middle ear. Therefore infections in the middle ear can easily +spread into the mastoid area. + + + + + +Tympanic membrane + +Cartilage + + + +Pharyngotympanic tube + +Nasopharynx + +Fig. 8.122 Pharyngotympanic tube. + + + + +In the clinic + +Mastoiditis +Infection within the mastoid antrum and mastoid cells is usually secondary to infection in the middle ear. The mastoid cells provide an excellent culture medium for infection. Infection of the bone (osteomyelitis) may also develop, spreading into the middle cranial fossa. +Drainage of the pus within the mastoid air cells is necessary and there are numerous approaches for doing this. When undertaking this type of surgery, it is extremely important that care is taken not to damage +the mastoid wall of the middle ear to prevent injury to the facial nerve [VII]. Any breach of the inner table of the cranial vault may allow bacteria to enter the cranial cavity and meningitis will ensue. + + +Pharyngotympanic tube +The pharyngotympanic tube connects the middle ear with the nasopharynx (Fig. 8.122) and equalizes pressure on both sides of the tympanic membrane. Its opening in the middle ear is on the anterior wall, and from here it extends forward, medially, and downward to enter the nasopharynx just posterior to the inferior meatus of the +950 nasal cavity. It consists of: + +■ a bony part (the one-third nearest the middle ear); and ■ a cartilaginous part (the remaining two-thirds). + +The opening of the bony part is clearly visible on the inferior surface of the skull at the junction of the squamous and petrous parts of the temporal bone immediately poste-rior to the foramen ovale and foramen spinosum. + +Vessels +The arterial supply to the pharyngotympanic tube is from several sources. Branches arise from the ascending pha-ryngeal artery (a branch of the external carotid artery) and from two branches of the maxillary artery (the middle meningeal artery and the artery of the pterygoid canal). +Venous drainage of the pharyngotympanic tube is to the pterygoid plexus of veins in the infratemporal fossa. + +Innervation +Innervation of the mucous membrane lining the pharyn-gotympanic tube is primarily from the tympanic plexus because it is continuous with the mucous membrane lining the tympanic cavity, the internal surface of the tympanic membrane, and the mastoid antrum and mastoid cells. This plexus receives its major contribution from the tym-panic nerve, a branch of the glossopharyngeal nerve [IX]. +Regional Anatomy • Ear 8 + + +Auditory ossicles +The bones of the middle ear consist of the malleus, incus, and stapes. They form an osseous chain across the middle ear from the tympanic membrane to the oval window of the internal ear (Fig. 8.123). + +Incus articulation + + +Muscles associated with the auditory ossicles modulate movement during the transmission of vibrations. + +Malleus +The malleus is the largest of the auditory ossicles and is attached to the tympanic membrane. Identifiable parts include the head of the malleus, neck of the malleus, + + + +Malleus articulation Head of malleus + +anterior and lateral processes, and handle of the malleus (Fig. 8.123). The head of the malleus is the + + + + + + + + +Lateral process + + +Short limb + +Neck of malleus + +Body of Anterior process incus + +B Long limb + +rounded upper part of the malleus in the epitympanic recess. Its posterior surface articulates with the incus. +Inferior to the head of the malleus is the constricted neck of the malleus, and below this are the anterior and lateral processes: + +■ The anterior process is attached to the anterior wall of the middle ear by a ligament. + + + +Handle of malleus +A Base of stapes + +■ The lateral process is attached to the anterior and pos-terior malleolar folds of the tympanic membrane. + + + +Posterior limb + + +C + + +Anterior limb + + +Head of stapes + +The downward extension of the malleus, below the anterior and lateral processes, is the handle of the malleus, which is attached to the tympanic membrane. + + +Fig. 8.123 Auditory ossicles. A. Malleus. B. Incus. C. Stapes. + +Malleus Incus + + + + +Tensor tympani muscle + + +Tendon of stapedius muscle +Pyramidal eminence + + + +Footplate of stapes + + + + + +Pharyngotympanic tube + + +Tympanic membrane + + + +Fig. 8.124 Muscles associated with the auditory ossicles (right ear). 951 +Head and Neck + + + + +Incus +The second bone in the series of auditory ossicles is the incus. It consists of the body of the incus and long and short limbs (Fig. 8.123): + +Innervation of the tensor tympani is by a branch from the mandibular nerve [V3]. +Contraction of the tensor tympani pulls the handle of the malleus medially. This tenses the tympanic membrane, reducing the force of vibrations in response to loud noises. + + + +■ The enlarged body of the incus articulates with the head of the malleus and is in the epitympanic recess. +■ The long limb extends downward from the body, paral-leling the handle of the malleus, and ends by bending medially to articulate with the stapes. +■ The short limb extends posteriorly and is attached by a ligament to the upper posterior wall of the middle ear. + +Stapedius +The stapedius muscle is a very small muscle that originates from inside the pyramidal eminence, which is a small projection on the mastoid wall of the middle ear (Fig. 8.124). Its tendon emerges from the apex of the pyramidal eminence and passes forward to attach to the posterior surface of the neck of the stapes. + + + + +Stapes +The stapes is the most medial bone in the osseous chain and is attached to the oval window. It consists of the head of the stapes, anterior and posterior limbs, and the base of the stapes (Fig. 8.123): + +The stapedius is innervated by a branch from the facial nerve [VII]. +Contraction of the stapedius muscle, usually in response to loud noises, pulls the stapes posteriorly and prevents excessive oscillation. + +Vessels + +■ The head of the stapes is directed laterally and articu- Numerous arteries supply the structures in the middle ear: lates with the long process of the incus. + +■ The two limbs separate from each other and attach to the oval base. +■ The base of the stapes fits into the oval window on the labyrinthine wall of the middle ear. + +■ the two largest branches are the tympanic branch of the maxillary artery and the mastoid branch of the occipital or posterior auricular arteries; +■ smaller branches come from the middle meningeal + + + + +Muscles associated with the ossicles +Two muscles are associated with the bony ossicles of the middle ear—the tensor tympani and stapedius (Fig. 8.124 and Table 8.10). + +Tensor tympani +The tensor tympani muscle lies in a bony canal above the pharyngotympanic tube. It originates from the cartilagi-nous part of the pharyngotympanic tube, the greater wing of the sphenoid, and its own bony canal, and passes through its canal in a posterior direction, ending in a rounded tendon that inserts into the upper part of the handle of the malleus. + +artery, the ascending pharyngeal artery, the artery of the pterygoid canal, and tympanic branches from the internal carotid artery. + +Venous drainage of the middle ear returns to the ptery-goid plexus of veins and the superior petrosal sinus. + +Innervation +The tympanic plexus innervates the mucous membrane lining the walls and contents of the middle ear, which includes the mastoid area and the pharyngotympanic tube. It is formed by the tympanic nerve, a branch of the glossopharyngeal nerve [IX], and from branches of the internal carotid plexus. The tympanic plexus occurs in the + + + + + +Table 8.10 + +Muscle + +Muscles of the middle ear + +Origin Insertion Innervation Function + + + +Tensor tympani + + + +Stapedius + +952 + +Cartilaginous part of pharyngotympanic tube, greater wing of sphenoid, its own bony canal +Attached to inside of pyramidal eminence + +Upper part of handle of malleus + + +Neck of stapes + +Branch from mandibular nerve [V3] + + +Branch of facial nerve [VII] + +Contraction pulls handle of malleus medially, tensing tympanic membrane + +Contraction pulls stapes posteriorly, preventing excessive oscillation +Regional Anatomy • Ear 8 + + +Prominence of facial canal + + + + + +Prominence of lateral semicircular canal + +Stapes +Tensor tympani muscle + +Lesser petrosal nerve + + + + + +Tympanic plexus + +Round window + + + + + +Pharyngotympanic tube + +Branch from internal carotid plexus (caroticotympanic nerve) +Tympanic nerve +Promontory (from glossopharyngeal nerve [IX]) + +Fig. 8.125 Innervation of the middle ear. + + +mucous membrane covering the promontory, which is the rounded bulge on the labyrinthine wall of the middle ear (Fig. 8.125). +As the glossopharyngeal nerve [IX] exits the skull through the jugular foramen, it gives off the tympanic nerve. This branch reenters the skull through a small foramen and passes through the bone to the middle ear. +Once in the middle ear, the tympanic nerve forms the tympanic plexus, along with branches from the plexus of nerves surrounding the internal carotid artery (caroticotympanic nerves). Branches from the tym-panic plexus supply the mucous membranes of the middle ear, including the pharyngotympanic tube and the + +mastoid area. +The tympanic plexus also gives off a major branch (the lesser petrosal nerve), which supplies preganglionic para-sympathetic fibers to the otic ganglion (Fig. 8.125). +The lesser petrosal nerve leaves the area of the promon-tory, exits the middle ear, travels through the petrous part of the temporal bone, and exits onto the anterior surface of the petrous part of the temporal bone through a hiatus just below the hiatus for the greater petrosal nerve (Fig. 8.126). It continues diagonally across the anterior surface of the temporal bone before exiting the middle cranial fossa through the foramen ovale. Once outside the skull it enters the otic ganglion. + + + + +Foramen ovale + +Groove and hiatus for greater petrosal nerve + +Groove and hiatus for lesser petrosal nerve + +Fig. 8.126 Grooves and hiatuses for the greater and lesser petrosal +nerves. 953 +Head and Neck + + + + +Internal ear +The internal ear consists of a series of bony cavities (the bony labyrinth) and membranous ducts and sacs (the membranous labyrinth) within these cavities. All these structures are in the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially (Figs. 8.127 and 8.128). +The bony labyrinth consists of the vestibule, three semicircular canals, and the cochlea (Fig. 8.128). These bony cavities are lined with periosteum and contain a clear fluid (the perilymph). +Suspended within the perilymph but not filling all spaces of the bony labyrinth is the membranous labyrinth, which consists of the semicircular ducts, the cochlear duct, and two sacs (the utricle and the saccule). These mem-branous spaces are filled with endolymph. +The structures in the internal ear convey information to the brain about balance and hearing: + + + + + + + + + + +Anterior semicircular canal + + + + + + + + + + + + + + + + + +Cochlea + + +Vestibulocochlear nerve [VIII] + + + +■ The cochlear duct is the organ of hearing. +■ The semicircular ducts, utricle, and saccule are the organs of balance. + +Posterior semicircular canal + + +Lateral semicircular canal + + +Fig. 8.127 Location of the internal ear in temporal bone. + +Semicircular canals Semicircular duct +Facial nerve [VII] + +Vestibular nerve +Vestibular ganglion + +Internal acoustic meatus + + + + + +Vestibule + + +Tympanic membrane + +Facial nerve [VII] +Vestibulocochlear nerve [VIII] + +Cochlear nerve + + +Cochlea + + + + + +Cochlear duct + + + + + + + + +Pharyngotympanic tube + +954 + +Fig. 8.128 Internal ear. +Regional Anatomy • Ear 8 + + + +The nerve responsible for these functions is the vestibu-locochlear nerve [VIII], which divides into vestibular (balance) and cochlear (hearing) parts after entering the internal acoustic meatus (Fig. 8.128). + +Bony labyrinth +The vestibule, which contains the oval window in its lateral wall, is the central part of the bony labyrinth (Fig. 8.129). It communicates anteriorly with the cochlea and postero-superiorly with the semicircular canals. +A narrow canal (the vestibular aqueduct) leaves the vestibule, and passes through the temporal bone to open on the posterior surface of the petrous part of the temporal bone. + +Semicircular canals +Projecting in a posterosuperior direction from the vestibule are the anterior, posterior, and lateral semicircular + +canals (Fig. 8.129). Each of these canals forms two-thirds of a circle connected at both ends to the vestibule and with one end dilated to form the ampulla. The canals are ori-ented so that each canal is at right angles to the other two. + +Cochlea +Projecting in an anterior direction from the vestibule is the cochlea, which is a bony structure that twists on itself two and one-half to two and three-quarter times around a central column of bone (the modiolus). This arrangement produces a cone-shaped structure with a base of the cochlea that faces posteromedially and an apex that faces anterolaterally (Fig. 8.130). This positions the wide base of the modiolus near the internal acoustic meatus, where it is entered by branches of the cochlear part of the vestibu-locochlear nerve [VIII]. +Extending laterally throughout the length of the modio-lus is a thin lamina of bone (the lamina of the modiolus, + + + + + + + +Posterior semicircular canal and duct + + + + + + +Ampulla + +Utricle + +Stapes in oval window + +Vestibule + + +Tympanic membrane + +Lateral semicircular canal and duct + +Anterior semicircular canal and duct Vestibular aqueduct +Dura mater + +Saccule + + + + + + +Helicotrema + + +Cochlea + +Scala vestibuli Cochlear duct +Scala tympani + + + + + +Round window + + +Opening of cochlear canaliculus + + +Pharyngotympanic tube + + +Fig. 8.129 Bony labyrinth. 955 +Head and Neck + + + +or spiral lamina). Circling around the modiolus, and held in a central position by its attachment to the lamina of the + +cochlea and are continuous with each other at the apex through a narrow slit (the helicotrema): + + + +modiolus, is the cochlear duct, which is a component of the membranous labyrinth. +Attached peripherally to the outer wall of the cochlea, the cochlear duct creates two canals (the scala vestibuli and the scala tympani), which extend throughout the + + +■ The scala vestibuli is continuous with the vestibule. +■ The scala tympani is separated from the middle ear by the secondary tympanic membrane covering the round window (Fig. 8.131). + + + + + + + +Modiolus + +Scala vestibuli + +Cochlear duct + +Scala tympani + +Finally, near the round window is a small channel (the cochlear canaliculus), which passes through the tempo- +Helicotrema ral bone and opens on its inferior surface into the posterior cranial fossa. This provides a connection between the perilymph-containing cochlea and the subarachnoid space (Fig. 8.131). + +Membranous labyrinth +The membranous labyrinth is a continuous system of ducts and sacs within the bony labyrinth. It is filled with endolymph and separated from the periosteum that covers the walls of the bony labyrinth by perilymph. +Consisting of two sacs (the utricle and the saccule) and four ducts (the three semicircular ducts and the cochlear duct), the membranous labyrinth has unique functions related to balance and hearing: + + + +Lamina of modiolus Cochlear nerve Spiral ganglion + +Fig. 8.130 Cochlea. + + +■ The utricle, saccule, and three semicircular ducts are part of the vestibular apparatus (i.e., organs of balance). +■ The cochlear duct is the organ of hearing. + + + + +Lateral semicircular canal and duct + +Posterior semicircular canal and duct + +Ampulla +Anterior semicircular canal and duct +Endolymphatic sac and duct +Dura mater + + +Saccule + + + + +Utricle + + +Helicotrema + + +Stapes in oval window + +Utricosaccular duct +Round window + +Opening of cochlear canaliculus + + + +Scala vestibuli Cochlear duct +Scala tympani + + + + + +956 Fig. 8.131 Membranous labyrinth. +Regional Anatomy • Ear 8 + + + +The general organization of the parts of the membra-nous labyrinth (Fig. 8.131) places: + + +Organ of hearing Cochlear duct + +■ the cochlear duct within the cochlea of the bony laby-rinth, anteriorly, +■ the three semicircular ducts within the three semicircu-lar canals of the bony labyrinth, posteriorly, and +■ the saccule and utricle within the vestibule of the bony labyrinth, in the middle. + + +The cochlear duct has a central position in the cochlea of the bony labyrinth dividing it into two canals (the scala vestibuli and the scala tympani). It is maintained in this position by being attached centrally to the lamina of the modiolus, which is a thin lamina of bone extending from the modiolus (the central bony core of the cochlea) and peripherally to the outer wall of the cochlea (Fig. 8.132). + + +Organs of balance +Five of the six components of the membranous labyrinth are concerned with balance. These are the two sacs (the utricle and the saccule) and three ducts (the anterior, posterior, and lateral semicircular ducts). + +Utricle, saccule, and endolymphatic duct +The utricle is the larger of the two sacs. It is oval, elongated and irregular in shape and is in the posterosuperior part of the vestibule of the bony labyrinth. +The three semicircular ducts empty into the utricle. Each semicircular duct is similar in shape, including a dilated end forming the ampulla, to its complementary bony semicircular canal, only much smaller. +The saccule is a smaller, rounded sac lying in the antero- + +Thus, the triangular-shaped cochlear duct has: + +■ an outer wall against the bony cochlea consisting of thickened, epithelial-lined periosteum (the spiral ligament), +■ a roof (the vestibular membrane), which separates the endolymph in the cochlear duct from the perilymph in the scala vestibuli and consists of a membrane with a connective tissue core lined on either side with epithe-lium, and +■ a floor, which separates the endolymph in the cochlear duct from the perilymph in the scala tympani and con-sists of the free edge of the lamina of the modiolus, and + + + +inferior part of the vestibule of the bony labyrinth (Fig. 8.131). The cochlear duct empties into it. + + +Modiolus +Scala vestibuli + +The utriculosaccular duct establishes continuity + +between all components of the membranous labyrinth and connects the utricle and saccule. Branching from this small duct is the endolymphatic duct, which enters the ves-tibular aqueduct (a channel through the temporal bone) to emerge onto the posterior surface of the petrous part of the temporal bone in the posterior cranial fossa. Here the endolymphatic duct expands into the endolymphatic sac, which is an extradural pouch that functions in resorp-tion of endolymph. + +Sensory receptors +Functionally, sensory receptors for balance are organized into unique structures that are located in each of the components of the vestibular apparatus. In the utricle and saccule the sense organ is the macula of the utricle and the macula of the saccule, respectively, and in the ampulla of each of the three semicircular ducts it is the crista. +The utricle responds to linear acceleration in the hori-zontal plane and sideways head tilts, while the saccule responds to linear acceleration in the vertical plane, such as forward-backward and upward-downward movements. + +Vestibular membrane + + +Spiral ligament + + + + + + + + + + + + + + + + + +Spiral organ + +Basilar membrane + + + + + + + + + + + + + + + + + + + + + +Lamina of modiolus + +Scala tympani + + + +In contrast, the receptors in the three semicircular ducts respond to rotational movement in any direction. + + +Fig. 8.132 Membranous labyrinth, cross section. 957 +Head and Neck + + + +a membrane (the basilar membrane) extending from this free edge of the lamina of the modiolus to an exten-sion of the spiral ligament covering the outer wall of the cochlea. + +The spiral organ is the organ of hearing, rests on the basilar membrane, and projects into the enclosed, endolymph-filled cochlear duct (Fig. 8.132). + +Vessels +The arterial supply to the internal ear is divided between vessels supplying the bony labyrinth and the membranous labyrinth. +The bony labyrinth is supplied by the same arteries that supply the surrounding temporal bone—these include an anterior tympanic branch from the maxillary artery, a stylomastoid branch from the posterior auricular artery, and a petrosal branch from the middle meningeal artery. +The membranous labyrinth is supplied by the labyrin-thine artery, which either arises from the anteroinferior cerebellar artery or is a direct branch of the basilar artery—whatever its origin, it enters the internal acoustic meatus with the facial [VII] and vestibulocochlear [VIII] nerves and eventually divides into: + + +parts, which distribute to the three semicircular ducts and the utricle and saccule (see Fig. 8.128). +The cochlear nerve enters the base of the cochlea and passes upward through the modiolus. The ganglion cells of the cochlear nerve are in the spiral ganglion at the base of the lamina of the modiolus as it winds around the modiolus (Fig. 8.130). Branches of the cochlear nerve pass through the lamina of the modiolus to innervate the recep-tors in the spiral organ. + + +Facial nerve [VII] in the temporal bone +The facial nerve [VII] is closely associated with the vestibu-locochlear nerve [VIII] as it enters the internal acoustic meatus of the temporal bone. Traveling through the tem-poral bone, its path and several of its branches are directly related to the internal and middle ears. +The facial nerve [VII] enters the internal acoustic meatus in the petrous part of the temporal bone (Fig. 8.133A). The vestibulocochlear nerve and the labyrinthine artery accompany it. +At the distal end of the internal acoustic meatus, the facial nerve [VII] enters the facial canal and continues laterally between the internal and middle ears. At this + + +■ a cochlear branch, which passes through the modio-lus and supplies the cochlear duct; and +■ one or two vestibular branches, which supply the vestibular apparatus. + +point the facial nerve [VII] enlarges and bends posteriorly and laterally. The enlargement is the sensory geniculate ganglion. As the facial canal continues, the facial nerve [VII] turns sharply downward, and running in an almost vertical direction, it exits the skull through the stylomas-toid foramen (Fig. 8.133A). + +Venous drainage of the membranous labyrinth is + +through vestibular veins and cochlear veins, which follow the arteries. These come together to form a labyrinthine vein, which eventually empties into either the inferior petrosal sinus or the sigmoid sinus. + +Innervation +The vestibulocochlear nerve [VIII] carries special afferent fibers for hearing (the cochlear component) and balance (the vestibular component). It enters the lateral surface of the brainstem, between the pons and medulla, after exiting the temporal bone through the internal acoustic meatus and crossing the posterior cranial fossa. +Inside the temporal bone, at the distal end of the internal + + +Branches +Greater petrosal nerve. At the geniculate ganglion, the facial nerve [VII] gives off the greater petrosal nerve (Fig. 8.133A). This is the first branch of the facial nerve [VII]. The greater petrosal nerve leaves the geniculate ganglion, travels anteromedially through the temporal bone, and emerges through the hiatus for the greater petrosal nerve on the anterior surface of the petrous part of the temporal bone (see Fig. 8.126). The greater petrosal nerve carries preganglionic parasympathetic fibers to the pterygopala-tine ganglion. +Continuing beyond the bend, the position of the facial + + + +acoustic meatus, the vestibulocochlear nerve divides to form: + +nerve [VII] is indicated on the medial wall of the middle ear by a bulge (see Fig. 8.125). + + + + +■ the cochlear nerve, and ■ the vestibular nerve. + +Nerve to stapedius and chorda tympani. Near the begin-ning of its vertical descent, the facial nerve [VII] gives off a small branch, the nerve to the stapedius (Fig. 8.133), which innervates the stapedius muscle, and just before it + + + +The vestibular nerve enlarges to form the vestibular 958 ganglion, before dividing into superior and inferior + +exits the skull the facial nerve [VII] gives off the chorda tympani nerve. +Regional Anatomy • Ear 8 + + +Geniculate ganglion + +Facial nerve [VII] + +Internal acoustic meatus + +Greater petrosal nerve + + + + + +Nerve to stapedius muscle + + + + +Chorda tympani + + + +Middle ear + +Stylomastoid foramen +A Incus + +Malleus + + + + + + + + +Chorda tympani + + + + + + + + +Tympanic membrane + + + +B + + +Fig. 8.133 A. Facial nerve in the temporal bone. B. Chorda tympani in the temporal bone. + + +959 +Head and Neck + + + +The chorda tympani does not immediately exit the temporal bone, but ascends to enter the middle ear through its posterior wall, passing near the upper aspect of the tympanic membrane between the malleus and incus (Fig. 8.133B). It then exits the middle ear through a canal leading to the petrotympanic fissure and exits the skull through this fissure to join the lingual nerve in the infra-temporal fossa. + +Transmission of sound +A sound wave enters the external acoustic meatus and strikes the tympanic membrane moving it medially (Fig. 8.134). As the handle of the malleus is attached to this membrane, it also moves medially. This moves the head of the malleus laterally. Because the heads of the malleus and incus articulate with each other, the head of the incus is also moved laterally. This pushes the long process of the incus medially. The long process articulates with the stapes, so its movement causes the stapes to move medially. In turn, because the base of the stapes is attached to the oval window, the oval window is also moved medially. + +This action completes the transfer of a large-amplitude, low-force, airborne wave that vibrates the tympanic mem-brane into a small-amplitude, high-force vibration of the oval window, which generates a wave in the fluid-filled scala vestibuli of the cochlea. +The wave established in the perilymph of the scala ves-tibuli moves through the cochlea and causes an outward bulging of the secondary tympanic membrane covering the round window at the lower end of the scala tympani (Fig. 8.134). This causes the basilar membrane to vibrate, which in turn leads to stimulation of receptor cells in the spiral organ. +The receptor cells send impulses back to the brain through the cochlear part of the vestibulocochlear nerve [VIII] where they are interpreted as sound. +If the sounds are too loud, causing excessive movement of the tympanic membrane, contraction of the tensor tympani muscle (attached to the malleus) and/or the sta-pedius muscle (attached to the stapes) dampens the vibra-tions of the ossicles and decreases the force of the vibrations reaching the oval window. + + + + + + + +Malleus Incus Helicotrema Vestibulocochlear nerve [VIII] + +Stapes + +Oval window External acoustic meatus Scala +vestibuli + + +Cochlear duct + + +Spiral organ + + + +Tympanic membrane + +Round window +Scala tympani + +Fig. 8.134 Transmission of sound. + + + + + + + + +960 +Regional Anatomy • Temporal and Infratemporal Fossae 8 + + + +TEMPORAL AND INFRATEMPORAL FOSSAE + +The temporal and infratemporal fossae are interconnected spaces on the lateral side of the head (Fig. 8.135). Their boundaries are formed by bone and soft tissues. +The temporal fossa is superior to the infratemporal fossa, above the zygomatic arch, and communicates with the infratemporal fossa below through the gap between the zygomatic arch and the more medial surface of the skull. +The infratemporal fossa is a wedge-shaped space deep to the masseter muscle and the underlying ramus of the + +mandible. Structures that travel between the cranial cavity, neck, pterygopalatine fossa, floor of the oral cavity, floor of the orbit, temporal fossa, and superficial regions of the head pass through it. +Of the four muscles of mastication (masseter, tempora-lis, medial pterygoid, and lateral pterygoid) that move the lower jaw at the temporomandibular joint, one (masseter) is lateral to the infratemporal fossa, two (medial and lateral pterygoid) are in the infratemporal fossa, and one fills the temporal fossa. + + + +Mandibular fossa + +Articular tubercle + +Zygomatic arch + +Temporal fossa + + +Groove for middle temporal artery + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Supramastoid crest + +External acoustic meatus + +Infratemporal fossa + + +Masseter muscle Ramus of mandible + +Fig. 8.135 Temporal and infratemporal fossae. 961 +Head and Neck + + + + +Bony framework +Bones that contribute significantly to the boundaries of the temporal and infratemporal fossae include the temporal, zygomatic, and sphenoid bones, and the maxilla and man-dible (Figs. 8.136 and 8.137). +Parts of the frontal and parietal bones are also involved. + +■ a transversely oriented supramastoid crest, which extends posteriorly from the base of the zygomatic process and marks the posteroinferior border of the temporal fossa; and +■ a vertically oriented groove for the middle temporal artery, a branch of the superficial temporal artery. + + + + +Temporal bone +The squamous part of the temporal bone forms part of the bony framework of the temporal and infratemporal fossae. The tympanic part of the temporal bone forms the posteromedial corner of the roof of the infratemporal fossa, and also articulates with the head of the mandible +to form the temporomandibular joint. +The lateral surface of the squamous part of the temporal + +Two features that participate in forming the temporo-mandibular joint on the inferior aspect of the root of the zygomatic process are the articular tubercle and the man-dibular fossa. Both are elongate from medial to lateral. Posterior to the mandibular fossa is the external acoustic meatus. The tympanic part of the temporal bone is a flat concave plate of bone that curves inferiorly from the back of the mandibular fossa and forms part of the wall of the external auditory meatus. + +bone is marked by two surface features on the medial wall When viewed from inferiorly, there is a distinct of the temporal fossa: tympanosquamous fissure between the tympanic and + + + + + + + +Foramen ovale + +Infratemporal crest + +Greater wing of sphenoid bone + +Frontal bone + +Frontal process of zygomatic bone + +Zygomaticotemporal foramen +(on deep surface of zygomatic bone) + +Zygomaticofacial foramen +Pterygopalatine fossa +Infratemporal surface of maxilla +Maxillary process of zygomatic bone +Zygomatic bone +Alveolar foramen + +Posterior surface of maxilla + +Squamous part of temporal bone + + +Foramen spinosum + +Articular tubercle +Mandibular fossa + + + +Groove for middle temporal artery +Supramastoid crest + +External acoustic meatus + + +Tympanomastoid fissure + + + +Mastoid process + + +Petrotympanic fissure + +Tympanic plate +Spine of sphenoid +Styloid process + + + +Palatine bone + +Lateral plate of pterygoid process of sphenoid bone + + + +Pterygoid hamulus + + +Pterygomaxillary fissure +(leading into pterygopalatine fossa) + + +962 Fig. 8.136 Bony features related to the temporal and infratemporal fossae. +Regional Anatomy • Temporal and Infratemporal Fossae 8 + + +Superior border Condylar process and curve superiorly. The inferior and lateral surfaces form the roof of the infratemporal fossa and the medial wall of the temporal fossa, respectively. +The sharply angled boundary between the lateral and + + +Anterior border + +Oblique line + + + +Body + +inferior surfaces of the greater wing is the infratemporal crest (Fig. 8.136). Two apertures (the foramen ovale +Ramus and the foramen spinosum) pass through the base of the greater wing and allow the mandibular nerve [V3] and the middle meningeal artery, respectively, to pass between the middle cranial fossa and infratemporal fossa. In addi-tion, one or more small sphenoidal emissary foramina +Angle penetrate the base of the greater wing anteromedial to the foramen ovale and allow emissary veins to pass between + + + +Inferior border +Mental foramen A +Pterygoid fovea +Head Mandibular notch + +the pterygoid plexus of veins in the infratemporal fossa and the cavernous sinus in the middle cranial fossa. +Projecting vertically downward from the greater wing immediately medial to the foramen spinosum is the irregularly shaped spine of the sphenoid, which is the + + + +Neck Coronoid process + +Mandibular foramen + +Lingula Mylohyoid groove +Mylohyoid line + + +Angle + +attachment site for the cranial end of the sphenomandibu-lar ligament. +The lateral plate of the pterygoid process is a vertically oriented sheet of bone that projects posterolaterally from the pterygoid process (Fig. 8.136). Its lateral and medial surfaces provide attachment for the lateral and medial pterygoid muscles, respectively. + +Maxilla +The posterior surface of the maxilla contributes to the + + + + +Roughening for attachment B of medial pterygoid muscle + +anterior wall of the infratemporal fossa (Fig. 8.136). This surface is marked by a foramen for the posterosuperior alveolar nerve and vessels. The superior margin forms the + +Fig. 8.137 Mandible. A. Lateral view of left side. B. Medial view of left side. + +inferior border of the inferior orbital fissure. + +Zygomatic bone +The zygomatic bone is a quadrangular-shaped bone that forms the palpable bony prominence of the cheek: + + + +squamous parts of the temporal bone. Medially, a small slip of bone from the petrous part of the temporal bone insinu-ates itself into the fissure and forms a petrotympanic fissure between it and the tympanic part (Fig. 8.136). +The chorda tympani nerve exits the skull and enters the infratemporal fossa through the medial end of the petro-tympanic fissure. + +Sphenoid bone +The parts of the sphenoid bone that form part of the bony + + +■ A maxillary process extends anteromedially to articu-late with the zygomatic process of the maxilla. +■ A frontal process extends superiorly to articulate with the zygomatic process of the frontal bone. +■ A temporal process extends posteriorly to articulate with the zygomatic process of the temporal bone to complete the zygomatic arch. + +A small zygomaticofacial foramen on the lateral surface + +framework of the infratemporal fossa are the lateral plate of the zygomatic bone transmits the zygomaticofacial + +of the pterygoid process and the greater wing (Fig. 8.136). The greater wing also forms part of the medial wall of the temporal fossa. +The greater wings extend one on each side from the body of the sphenoid. They project laterally from the body + +nerve and vessels onto the cheek. +A thin plate of bone extends posteromedially from the frontal process and contributes to the lateral wall of the orbit on one side and the anterior wall of the temporal +fossa on the other. A zygomaticotemporal foramen on the 963 +Head and Neck + + + +temporal fossa surface of the plate where it attaches to the frontal process is for the zygomaticotemporal nerve. + +Ramus of mandible +The ramus of the mandible is quadrangular in shape and has medial and lateral surfaces and condylar and coro- + +The medial surface of the ramus of the mandible is the lateral wall of the infratemporal fossa (Fig. 8.137B). Its most distinctive feature is the mandibular foramen, which is the superior opening of the mandibular canal. The inferior alveolar nerve and vessels pass through this foramen. + +noid processes (Fig. 8.137). Immediately anterosuperior to the mandibular + +The lateral surface of the ramus of the mandible is generally smooth except for the presence of a few obliquely oriented ridges. Most of the lateral surface provides attach-ment for the masseter muscle. +The posterior and inferior borders of the ramus intersect to form the angle of the mandible, while the superior border is notched to form the mandibular notch. The anterior border is sharp and is continuous below with the + +foramen is a triangular elevation (the lingula) for attach-ment of the mandibular end of the sphenomandibular ligament. +An elongate groove (the mylohyoid groove) extends anteroinferiorly from the mandibular foramen. The nerve to the mylohyoid is in this groove. +Posteroinferior to the mylohyoid groove and mandibular foramen, the medial surface of the ramus of the mandible + + + +oblique line on the body of the mandible. +The coronoid process extends superiorly from the junction of the anterior and superior borders of the ramus. It is a flat, triangular process that provides attachment for the temporalis muscle. + +is roughened for attachment of the medial pterygoid muscle. + + +Temporomandibular joints + + + +The condylar process extends superiorly from the posterior and superior borders of the ramus. It consists of: + +The temporomandibular joints, one on each side, allow opening and closing of the mouth and complex chewing or side-to-side movements of the lower jaw. + + + +■ the head of the mandible, which is expanded medi-ally and participates in forming the temporomandibular joint; and +■ the neck of the mandible, which bears a shallow depression (the pterygoid fovea) on its anterior surface for attachment of the lateral pterygoid muscle. + +Each joint is synovial and is formed between the head of the mandible and the articular fossa and articular tubercle of the temporal bone (Fig. 8.138A). +Unlike most other synovial joints where the articular surfaces of the bones are covered by a layer of hyaline cartilage, those of the temporomandibular joint are covered + + + + +Upper joint cavity +Mandibular fossa Articular disc + + + + + + + + + + + +Synovial membrane + +Capsule + +Fibrocartilage on articular surface +Lower joint cavity + + +Lateral pterygoid muscle + + + + + + + + + + + + + + +Protrusion + + + +Depression + + +Forward movement of disc and mandible at upper joint + + + + + + + + + + + + +Hinge movement at lower joint + +A Articular tubercle B 964 Fig. 8.138 Temporomandibular joint. A. Mouth closed. B. Mouth open. +Regional Anatomy • Temporal and Infratemporal Fossae 8 + + + +by fibrocartilage. In addition, the joint is completely divided by a fibrous articular disc into two parts: + + +Movements of the mandible + + + + +■ The lower part of the joint allows mainly the hinge-like depression and elevation of the mandible. +■ The upper part of the joint allows the head of the man-dible to translocate forward (protrusion) onto the articu-lar tubercle and backward (retraction) into the mandibular fossa. + +A chewing or grinding motion occurs when the movements at the temporomandibular joint on one side are coordinated with a reciprocal set of movements at the joint on the other side. Movements of the mandible include depression, eleva-tion, protrusion, and retraction (Fig. 8.140): + + +Lateral ligament + + +Opening the mouth involves both depression and pro- Sphenomandibular ligament Capsule trusion (Fig. 8.138B). +The forward or protrusive movement allows greater depression of the mandible by preventing backward movement of the angle of the mandible into structures in the neck. + +Joint capsule +The synovial membrane of the joint capsule lines all nonarticular surfaces of the upper and lower compart-ments of the joint and is attached to the margins of the articular disc. +The fibrous membrane of the joint capsule encloses the temporomandibular joint complex and is attached: + +■ above along the anterior margin of the articular +tubercle, Stylomandibular ligament ■ laterally and medially along the margins of the articular +fossa, +■ posteriorly to the region of the tympanosquamous + +suture, and +■ below around the upper part of the neck of the mandible. + + +Fig. 8.139 Ligaments associated with the temporomandibular joint. + + + +The articular disc attaches around its periphery to the inner aspect of the fibrous membrane. + +Extracapsular ligaments +Three extracapsular ligaments are associated with the temporomandibular joint—the lateral, sphenomandibular, and the stylomandibular ligaments (Fig. 8.139): + +Protrusion +• Lateral pterygoid assisted by medial pterygoid + + + + +■ The lateral ligament is closest to the joint, just lateral to the capsule, and runs diagonally backward from the margin of the articular tubercle to the neck of the mandible. +■ The sphenomandibular ligament is medial to the temporomandibular joint, runs from the spine of the sphenoid bone at the base of the skull to the lingula on the medial side of the ramus of the mandible. +■ The stylomandibular ligament passes from the styloid process of the temporal bone to the posterior margin and angle of the mandible. + +Retraction +• Posterior fibers of temporalis, deep part of masseter, and geniohyoid and digastric + + +Elevation +• Temporalis, masseter, medial pterygoid +Depression • Gravity +• Digastric, geniohyoid, and mylohyoid muscles +Fig. 8.140 Movements of the temporomandibular joint. 965 +Head and Neck + + + +■ Depression is generated by the digastric, geniohyoid, and mylohyoid muscles on both sides, is normally assisted by gravity, and, because it involves forward movement of the head of the mandible onto the articular tubercle, the lateral pterygoid muscles are also involved. +■ Elevation is a very powerful movement generated by the temporalis, masseter, and medial pterygoid muscles and also involves movement of the head of the mandible into the mandibular fossa. +■ Protraction is mainly achieved by the lateral pterygoid muscle, with some assistance by the medial pterygoid. +■ Retraction is carried out by the geniohyoid and digastric muscles, and by the posterior and deep fibers of the temporalis and masseter muscles, respectively. + + + + + +Deep part + + + +Superficial part + + + + + +Masseteric artery +Masseteric nerve + + +Except for the geniohyoid muscle, which is innervated +by the C1 spinal nerve, all muscles that move the temporo- Mandibular notch mandibular joints are innervated by the mandibular nerve +[V3] by branches that originate in the infratemporal fossa. + +Masseter muscle +The masseter muscle is a powerful muscle of mastication that elevates the mandible (Fig. 8.141 and Table 8.11). It +overlies the lateral surface of the ramus of the mandible. Fig. 8.141 Masseter muscle. + + + + + + + + + + + +Table 8.11 + +Muscle Masseter + + +Temporalis + +Muscles of mastication + +Origin +Zygomatic arch and maxillary process of the zygomatic bone +Bone of temporal fossa and temporal fascia + + + +Insertion +Lateral surface of ramus of mandible + +Coronoid process of mandible and anterior margin of ramus of mandible almost to last molar tooth + + + +Innervation +Masseteric nerve from the anterior trunk of the mandibular nerve [V3] +Deep temporal nerves from the anterior trunk of the mandibular nerve [V3] + + + +Function +Elevation of mandible + + +Elevation and retraction of mandible + + + +Medial pterygoid + + + + + +Lateral pterygoid + + + +966 + +Deep head—medial surface of lateral plate of pterygoid process and pyramidal process of palatine bone; superficial head—tuberosity of the maxilla and pyramidal process of palatine bone +Upper head—roof of infratemporal fossa; lower head—lateral surface of lateral plate of the pterygoid process + +Medial surface of mandible near angle + + + + + +Capsule of temporomandibular joint in the region of attachment to the articular disc and to the pterygoid fovea on the neck of mandible + +Nerve to medial pterygoid from the mandibular nerve [V3] + + + + +Nerve to lateral pterygoid directly from the anterior trunk of the mandibular nerve [V3] or from the buccal branch + +Elevation and side-to-side movements of the mandible + + + + + +Protrusion and side-to-side movements of the mandible +Regional Anatomy • Temporal and Infratemporal Fossae 8 + + + +The masseter muscle is quadrangular in shape and is anchored above to the zygomatic arch and below to most of the lateral surface of the ramus of the mandible. +The more superficial part of the masseter originates + + +Temporal fossa +The temporal fossa is a narrow fan-shaped space that covers the lateral surface of the skull (Fig. 8.142A): + + + +from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic process of the maxilla. It inserts into the angle of the mandible and related poste-rior part of the lateral surface of the ramus of the mandible. +The deep part of the masseter originates from the medial aspect of the zygomatic arch and the posterior part of its inferior margin and inserts into the central and upper part of the ramus of the mandible as high as the coronoid process. +The masseter is innervated by the masseteric nerve from the mandibular nerve [V3] and supplied with blood by the masseteric artery from the maxillary artery. +The masseteric nerve and artery originate in the infra-temporal fossa and pass laterally over the margin of the mandibular notch to enter the deep surface of the masseter muscle. + + +■ Its upper margin is defined by a pair of temporal lines that arch across the skull from the zygomatic process of the frontal bone to the supramastoid crest of the tempo-ral bone. +■ It is limited laterally by the temporal fascia, which is a tough, fan-shaped aponeurosis overlying the tempo-ralis muscle and attached by its outer margin to the superior temporal line and by its inferior margin to the zygomatic arch. +■ Anteriorly, it is limited by the posterior surface of the frontal process of the zygomatic bone and the posterior surface of the zygomatic process of the frontal bone, which separate the temporal fossa behind from the orbit in front. + + + + + + + + + +Zygomatic process of frontal bone + +Superior temporal line +Inferior temporal line + + + + + +Temporal fascia + +Temporal fossa + + + + + + + +Supramastoid crest of temporal bone + + + + + +Zygomatic arch +Frontal process of zygomatic bone +A + +Infratemporal crest of sphenoid + + + + +B + + +Infratemporal fossa + + +Fig. 8.142 Temporal fossa. A. Lateral view. B. Lateral view showing the infratemporal fossa. 967 +Head and Neck + + + +■ Its inferior margin is marked by the zygomatic arch laterally and by the infratemporal crest of the greater wing of the sphenoid medially (Fig. 8.142B)—between these two features, the floor of the temporal fossa is open medially to the infratemporal fossa and laterally to the region containing the masseter muscle. + +from the bony surfaces of the fossa superiorly to the inferior temporal line and is attached laterally to the surface of the temporal fascia. The more anterior fibers are oriented verti-cally while the more posterior fibers are oriented horizon-tally. The fibers converge inferiorly to form a tendon, which passes between the zygomatic arch and the infratemporal crest of the greater wing of the sphenoid to insert on the + + +Contents +The major structure in the temporal fossa is the temporalis muscle. +Also passing through the fossa is the zygomaticotempo-ral branch of the maxillary nerve [V2], which enters the region through the zygomaticotemporal foramen on the temporal fossa surface of the zygomatic bone. + +Temporalis muscle +The temporalis muscle is a large, fan-shaped muscle that fills much of the temporal fossa (Fig. 8.143). It originates + +coronoid process of the mandible. +The temporalis muscle attaches down the anterior surface of the coronoid process and along the related margin of the ramus of the mandible, almost to the last molar tooth. +The temporalis is a powerful elevator of the mandible. Because this movement involves posterior translocation of the head of the mandible from the articular tubercle of the temporal bone and back into the mandibular fossa, the temporalis also retracts the mandible or pulls it posteriorly. In addition, the temporalis participates in side-to-side movements of the mandible. + + + + + +Superior temporal line +Inferior temporal line + + +Cut temporal fascia + + + + + + + + + + + + + + + + + + +Temporalis muscle + + + + +Coronoid process + + +968 Fig. 8.143 Temporalis muscle. Lateral view. +Regional Anatomy • Temporal and Infratemporal Fossae 8 + + + +The temporalis is innervated by deep temporal nerves that originate from the mandibular nerve [V3] in the infra-temporal fossa and then pass into the temporal fossa. +Blood supply of the temporalis is by deep temporal arter-ies, which travel with the nerves, and the middle temporal artery, which penetrates the temporal fascia at the posterior end of the zygomatic arch. + +Deep temporal nerves +The deep temporal nerves, usually two in number, originate from the anterior trunk of the mandibular nerve [V3] in the infratemporal fossa (Fig. 8.144). They pass superiorly and around the infratemporal crest of the greater wing of the sphenoid to enter the temporal fossa deep to the temporalis muscle, and supply the temporalis muscle. + +Zygomaticotemporal nerve +The zygomaticotemporal nerve is a branch of the zygomatic nerve (see Fig. 8.87, p. 922). The zygomatic nerve is a branch of the maxillary nerve [V2], which originates in the pterygopalatine fossa and passes into the orbit. + +The zygomaticotemporal nerve enters the temporal fossa through one or more small foramina on the temporal fossa surface of the zygomatic bone. +Branches of the zygomaticotemporal nerve pass superi-orly between the bone and the temporalis muscle to pene-trate the temporal fascia and supply the skin of the temple (Fig. 8.144). + +Deep temporal arteries +Normally two in number, these vessels originate from the maxillary artery in the infratemporal fossa and travel with the deep temporal nerves around the infratemporal crest of the greater wing of the sphenoid to supply the temporalis muscle (Fig. 8.144). They anastomose with branches of the middle temporal artery. + +Middle temporal artery +The middle temporal artery originates from the superficial temporal artery just superior to the root of the zygomatic arch between this structure and the external ear (Fig. 8.144). It penetrates the temporalis fascia, passes under + + + + + +Temporal fascia + + +Temporalis muscle + + + + + + +Zygomaticotemporal nerve (branch of maxillary nerve [V2]) +Middle temporal artery + +Superficial temporal artery + +Zygomaticofacial nerve + +Deep temporal arteries +Deep temporal nerves +Mandibular nerve [V3] + + + + +External carotid artery + + +Infratemporal crest Maxillary artery in infratemporal fossa + +Fig. 8.144 Nerves and arteries of the temporal fossa. 969 +Head and Neck + + + +the margin of the temporalis muscle, and travels superiorly on the deep surface of the temporalis muscle. +The middle temporal artery supplies the temporalis and anastomoses with branches of the deep temporal arteries. + + +Infratemporal fossa + +■ The medial wall is formed anteriorly by the lateral plate of the pterygoid process and more posteriorly by the pharynx and by two muscles of the soft palate (tensor and levator veli palatini muscles), and contains the pterygomaxillary fissure anteriorly, which allows structures to pass between the infratemporal and ptery-gopalatine fossae. +■ The anterior wall is formed by part of the posterior + +The wedge-shaped infratemporal fossa is inferior to the surface of the maxilla and contains the alveolar + +temporal fossa and between the ramus of the mandible laterally and the wall of the pharynx medially. It has a roof, a lateral wall, and a medial wall, and is open to the neck posteroinferiorly (Fig. 8.145): + +foramen, and the upper part opens as the inferior orbital fissure into the orbit. + + +Contents + + + +■ The roof is formed by the inferior surfaces of the greater wing of the sphenoid and the temporal bone, contains the foramen spinosum, foramen ovale, and the petro-tympanic fissure, and lateral to the infratemporal crest of the greater wing of the sphenoid, is open superiorly to the temporal fossa. +■ The lateral wall is the medial surface of the ramus + +Major contents of the infratemporal fossa include the sphenomandibular ligament, medial and lateral pterygoid muscles (Table 8.11), the maxillary artery, the mandibular nerve [V3], branches of the facial nerve [VII] and the glos-sopharyngeal nerve [IX], and the pterygoid plexus of veins. + +Sphenomandibular ligament + +of the mandible, which contains the opening to the The sphenomandibular ligament is an extracapsular mandibular canal. ligament of the temporomandibular joint. It is attached + + +Infratemporal crest Foramen ovale Foramen spinosum Greater wing of sphenoid bone + +Pterygopalatine fossa +Petrotympanic fissure + +Pterygomaxillary fissure (leading into pterygopalatine fossa) + +Lateral plate of pterygoid process + + +Tensor veli palatini Alveolar foramen +Levator veli palatini + +Posterior surface of maxilla + + +Head and neck of mandible + + + +Spine of sphenoid + +Superior constrictor + + + +Pharynx + + + +Pterygomandibular raphe Middle constrictor + + +Masseter + +Mylohyoid Hyoglossus + \ No newline at end of file