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+Function: motor Subscapularis, teres major
+
+
+
+
+Function: motor Deltoid, teres minor Function: sensory
+Skin over upper lateral part of arm
+
+Function: motor
+All muscles in the posterior compartments of arm and forearm Function: sensory
+Skin on the posterior aspects of the arm and forearm, the lower lateral surface of the arm, and the dorsal lateral surface of the hand
+
+
+
+
+
+
+734
+Regional Anatomy  •  Axilla	7
+
+
+The   median   nerve   continues   into   the   hand   to       of these three nerves and passes vertically along the poste-innervate:                                                                                       rior axillary wall. It penetrates and innervates the latissimus
+
+
+■     the three thenar muscles associated with the thumb,
+■     the two lateral lumbrical muscles associated with move-ment of the index and middle fingers, and
+■     the skin over the palmar surface of the lateral three and one-half digits and over the lateral side of the palm and middle of the wrist.
+
+The musculocutaneous nerve, the lateral root of  the
+
+dorsi muscle. The inferior subscapular nerve also passes inferiorly along the posterior axillary wall and innervates the subscapularis and teres major muscles.
+The axillary nerve originates from the posterior cord and  passes  inferiorly  and  laterally  along  the  posterior wall to exit the axilla through the quadrangular space (Fig. 7.56). It passes posteriorly around the surgical neck of the humerus and innervates both the deltoid and teres minor muscles. A superior lateral cutaneous nerve of
+
+
+
+median nerve, the median nerve, the medial root of the median  nerve,  and  the  ulnar  nerve  form  an  M  over the third part of the axillary artery (Fig. 7.55). This feature, together with penetration of the coracobrachialis muscle by the musculocutaneous nerve, can be used to identify components of the brachial plexus in the axilla.
+
+Branches of the posterior cord
+Five nerves originate from the posterior cord of the brachial plexus:
+
+the arm originates from the axillary nerve after passing through the quadrangular space and loops around the posterior margin of the deltoid muscle to innervate skin in that region. The axillary nerve is accompanied by the posterior circumflex humeral artery.
+The radial nerve is the largest terminal branch of the posterior cord (Fig. 7.56). It passes out of the axilla and into the posterior compartment of  the arm by passing through the triangular interval between the inferior border of  the teres major muscle, the long head of  the triceps
+
+
+
+
+■     the superior subscapular nerve, ■     the thoracodorsal nerve,
+■     the inferior subscapular nerve, ■     the axillary nerve, and
+■     the radial nerve (Fig. 7.53).
+
+brachii muscle, and the shaft of the humerus. It is accom-panied through the triangular interval by the profunda brachii artery, which originates from the brachial artery in the anterior compartment of the arm. The radial nerve and its branches innervate:
+
+
+
+
+All these nerves except the radial nerve innervate muscles associated with the shoulder region or the posterior wall of the axilla; the radial nerve passes into the arm and forearm. The superior subscapular, thoracodorsal, and inferior subscapular nerves originate sequentially from the poste-rior cord and pass directly into muscles associated with the
+
+■     all muscles in the posterior compartments of the arm and forearm, and
+■     the skin on the posterior aspect of the arm and forearm, the lower lateral surface of  the arm, and the dorsal lateral surface of the hand.
+
+The posterior cutaneous nerve of the arm (poste-
+
+
+
+posterior axillary wall (Fig. 7.56). The superior subscapu-lar nerve is short and passes into and supplies the sub-scapularis muscle. The thoracodorsal nerve is the longest
+
+rior  brachial  cutaneous  nerve)  originates  from  the radial nerve in the axilla and innervates skin on the poste-rior surface of the arm.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+735
+Upper Limb
+
+
+
+
+
+
+
+
+
+
+
+
+
+Superior subscapular nerve Axillary nerve
+
+Inferior subscapular nerve Radial nerve
+Posterior cutaneous nerve of arm
+
+Thoracodorsal nerve
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 7.56  Branches of the posterior cord of the brachial plexus.
+
+
+
+
+
+In the clinic
+
+Injuries to the brachial plexus
+The brachial plexus is an extremely complex structure. When damaged, it requires meticulous clinical history taking and examination. Assessment of the individual nerve functions can be obtained by nerve conduction studies and electromyography, which assess the latency of muscle contraction when the nerve is artificially stimulated.
+Brachial plexus injuries are usually the result of blunt 736	trauma producing nerve avulsions and disruption. These
+
+
+
+injuries are usually devastating for the function of the upper limb and require many months of dedicated rehabilitation for even a small amount of function to return.
+Spinal cord injuries in the cervical region and direct pulling injuries tend to affect the roots of the brachial plexus. Severe trauma to the first rib usually affects the trunks. The divisions and cords of the brachial plexus can be injured by dislocation of the glenohumeral joint.
+Regional Anatomy  •  Axilla	7
+
+
+
+
+Lymphatics
+All lymphatics from the upper limb drain into lymph nodes
+
+The 20–30 axillary nodes are generally divided into five groups on the basis of location.
+
+
+
+in the axilla (Fig. 7.57).
+In addition, axillary nodes receive drainage from an extensive  area  on  the  adjacent  trunk,  which  includes regions of the upper back and shoulder, the lower neck, the chest, and the upper anterolateral abdominal wall. Axil-lary nodes also receive drainage from approximately 75% of the mammary gland.
+
+■     Humeral (lateral) nodes posteromedial to the axillary vein receive most of the lymphatic drainage from the upper limb.
+■     Pectoral (anterior) nodes occur along the inferior margin of the pectoralis minor muscle along the course of the lateral thoracic vessels and receive drainage from the abdominal wall, the chest, and the mammary gland.
+
+
+
+
+Anterior scalene
+
+Apical nodes	Right subclavian trunk Infraclavicular nodes
+
+Some of upper limb
+
+Central nodes
+
+Pectoral nodes
+
+
+
+
+
+Superior part of mammary gland
+
+Humeral nodes
+
+Subscapular nodes
+
+
+
+Most of upper limb
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Anterolateral body wall and centrolateral part of mammary gland
+
+Fig. 7.57  Lymph nodes and vessels in the axilla.	737
+Upper Limb
+
+
+
+■     Subscapular (posterior) nodes on the posterior axil-lary wall in association with the subscapular vessels drain the posterior axillary wall and receive lymphatics from the back, the shoulder, and the neck.
+■     Central nodes are embedded in axillary fat and receive tributaries  from  humeral,  subscapular,  and  pectoral groups of nodes.
+■     Apical nodes are the most superior group of nodes in the axilla and drain all other groups of  nodes in the region. In addition, they receive lymphatic vessels that
+
+
+Axillary process of the mammary gland
+Although  the  mammary  gland  is  in  superficial  fascia overlying the thoracic wall, its superolateral region extends along the inferior margin of the pectoralis major muscle toward the axilla. In some cases, this may pass around the margin of the muscle to penetrate deep fascia and enter the axilla (Fig. 7.58). This axillary process rarely reaches as high as the apex of the axilla.
+
+accompany the cephalic vein as well as vessels that
+drain the superior region of the mammary gland.	Axillary process	Breast
+
+Efferent vessels from the apical group converge to form the  subclavian  trunk,  which  usually  joins  the  venous system at the junction between the right subclavian vein and the right internal jugular vein in the neck. On the left, the subclavian trunk usually joins the thoracic duct in the base of the neck.
+
+
+
+In the clinic
+
+Breast cancer
+Lymphatic drainage from the lateral part of the breast passes through nodes in the axilla. Significant disruption to the normal lymphatic drainage of the upper limb may occur if a mastectomy or a surgical axillary nodal clearance has been carried out for breast cancer. Furthermore, some patients have radiotherapy to the axilla to prevent the spread of metastatic disease, but a side effect of this is the destruction of the tiny lymphatics as well as the cancer cells.
+If the lymphatic drainage of the upper limb is damaged, the arm may swell and pitting edema
+(lymphedema) may develop.	Fig. 7.58  Axillary process of the breast.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+738
+Regional Anatomy  •  Arm	7
+
+
+
+ARM
+
+The arm is the region of the upper limb between the shoul-der and the elbow (Fig. 7.59). The superior aspect of the arm communicates medially with the axilla. Inferiorly, a number of important structures pass between the arm and the forearm through the cubital fossa, which is positioned anterior to the elbow joint.
+The arm is divided into two compartments by medial and lateral intermuscular septa, which pass from each side
+
+of the humerus to the outer sleeve of deep fascia that sur-rounds the limb (Fig. 7.59).
+The anterior compartment of the arm contains muscles that  predominantly  flex  the  elbow  joint;  the  posterior compartment  contains  muscles  that  extend  the  joint. Major nerves and vessels supply and pass through each compartment.
+
+
+
+
+
+Axilla
+
+
+
+
+
+
+Arm
+
+Line of section
+
+
+
+
+
+
+Forearm
+
+
+
+
+
+A
+
+Cubital fossa
+
+Lateral intermuscular septum
+
+Anterior (flexor) compartment
+Deep fascia
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Humerus
+
+B
+
+
+Medial intermuscular septum
+
+Posterior (extensor) compartment
+
+
+Fig. 7.59  Arm. A. Proximal and distal relationships. B. Transverse section through the middle of the arm.	739
+Upper Limb
+
+
+
+
+Bones
+The skeletal support for the arm is the humerus (Fig. 7.60). Most of the large muscles of the arm insert into the proxi-mal ends of the two bones of the forearm, the radius and the ulna, and flex and extend the forearm at the elbow joint. In addition, the muscles predominantly situated in the forearm that move the hand originate at the distal end of the humerus.
+
+Shaft and distal end of the humerus
+In cross section, the shaft of  the humerus is somewhat triangular with:
+
+of the lateral head of the triceps brachii muscle, beginning just inferior to the surgical neck and passing diagonally across the bone to the deltoid tuberosity.
+The middle part of the posterior surface and adjacent part of the anterolateral surface are marked by the shallow radial groove, which passes diagonally down the bone and parallel to the sloping posterior margin of the deltoid tuberosity.  The  radial  nerve  and  the  profunda  brachii artery lie in this groove.
+Approximately in the middle of  the shaft, the medial border is marked by thin elongate roughening for the attachment of the coracobrachialis muscle.
+Intermuscular septa, which separate the anterior com-
+
+
+■     anterior, lateral, and medial borders, and
+■     anterolateral,  anteromedial,  and  posterior  sur-
+
+partment from the posterior compartment, attach to the medial and lateral borders (Fig. 7.61).
+
+faces (Fig. 7.60).	Lateral intermuscular septum	Medial intermuscular septum
+
+
+The posterior surface of the humerus is marked on its superior aspect by a linear roughening for the attachment
+
+
+Anterior compartment
+
+Anterior view	Posterior compartment
+
+
+
+Head	Greater tubercle
+
+
+
+
+
+
+Attachment for lateral head
+of triceps brachii
+
+Radial groove
+Deltoid tuberosity
+
+Attachment for coracobrachialis
+
+
+
+Antero-medial surface
+
+
+
+
+
+
+Medial border
+
+
+
+
+Anterior border
+
+
+
+
+
+
+Posterior surface
+
+
+
+Antero-lateral surface
+
+
+
+
+
+
+Lateral border
+
+Lateral supra-epicondylar ridge
+
+
+
+
+Radial fossa
+
+
+Lateral epicondyle
+Capitulum    Trochlea
+
+
+
+
+
+
+Coronoid fossa
+
+
+
+
+Medial supraepicondylar ridge
+
+Medial
+Condyle	epicondyle
+
+Posterior view
+
+
+
+Posterior view
+
+Olecranon fossa
+
+
+Distal end	Trochlea
+
+
+
+740	Fig. 7.60  Humerus. Posterior view.	Fig. 7.61  Distal end of the humerus.
+Regional Anatomy  •  Arm	7
+
+
+
+Distally, the bone becomes flattened, and these borders expand as the lateral supraepicondylar ridge (lateral supracondylar ridge) and the medial supraepicondy-lar  ridge (medial  supracondylar  ridge). The lateral supraepicondylar  ridge  is  more  pronounced  than  the medial  ridge  and  is  roughened  for  the  attachment  of muscles found in the posterior compartment of the forearm. The distal end of the humerus, which is flattened in the anteroposterior plane, bears a condyle, two epicondyles,
+and three fossae, as follows (Fig. 7.61).
+
+The condyle
+The two articular parts of the condyle, the capitulum and the trochlea, articulate with the two bones of the forearm.
+
+These three fossae accommodate projections from the bones in the forearm during movements of  the elbow joint.
+
+Proximal end of the radius
+The proximal end of the radius consists of a head, a neck, and the radial tuberosity (Fig. 7.62A,B).
+The head of the radius is a thick disc-shaped structure oriented in the horizontal plane. The circular superior surface is concave for articulation with the capitulum of the humerus. The thick margin of the disc is broad medi-ally where it articulates with the radial notch on the proxi-mal end of the ulna.
+The neck of the radius is a short and narrow cylinder
+
+The  capitulum  articulates  with  the  radius  of  the	of bone between the expanded head and the radial tuberos-
+
+forearm. Lateral in position and hemispherical in shape, it projects anteriorly and somewhat inferiorly and is not visible when the humerus is viewed from the posterior aspect.
+The trochlea articulates with the ulna of the forearm. It is pulley shaped and lies medial to the capitulum. Its medial edge is more pronounced than its lateral edge and, unlike the capitulum, it extends onto the posterior surface of the bone.
+
+The two epicondyles
+The two epicondyles lie adjacent, and somewhat superior, to the trochlea and capitulum (Fig. 7.61).
+The medial epicondyle, a large bony protuberance, is the major palpable landmark on the medial side of  the elbow, and projects medially from the distal end of  the humerus. On its surface, it bears a large oval impression for the attachment of  muscles in the anterior compart-ment of the forearm. The ulnar nerve passes from the arm into the forearm around the posterior surface of the medial epicondyle and can be palpated against the bone in this location.
+The lateral epicondyle is much less pronounced than the medial epicondyle. It is lateral to the capitulum and has a large irregular impression for the attachment of muscles in the posterior compartment of the forearm.
+
+The three fossae
+Three fossae occur superior to the trochlea and capitulum on the distal end of the humerus (Fig. 7.61).
+The radial fossa is the least distinct of the fossae and occurs  immediately  superior  to  the  capitulum  on  the anterior surface of the humerus.
+The coronoid fossa is adjacent to the radial fossa and is superior to the trochlea.
+The largest of the fossae, the olecranon fossa, occurs immediately  superior  to  the  trochlea  on  the  posterior surface of the distal end of the humerus.
+
+ity on the shaft.
+The radial tuberosity is a large blunt projection on the medial surface of  the radius immediately inferior to the neck. Much of its surface is roughened for the attachment of the biceps brachii tendon. The oblique line of the radius continues diagonally across the shaft of the bone from the inferior margin of the radial tuberosity.
+
+Proximal end of the ulna
+The proximal end of  the ulna is much larger than the proximal end of the radius and consists of the olecranon, the coronoid process, the trochlear notch, the radial notch, and the tuberosity of the ulna (Fig. 7.63A,B).
+The  olecranon  is  a  large  projection  of  bone  that extends proximally from the ulna. Its anterolateral surface is articular and contributes to the formation of the troch-lear notch, which articulates with the trochlea of  the humerus.  The  superior  surface  is  marked  by  a  large roughened impression for the attachment of  the triceps brachii muscle. The posterior surface is smooth, shaped somewhat triangularly, and can be palpated as the “tip of the elbow.”
+The coronoid  process projects anteriorly from the proximal end of  the ulna (Fig. 7.63). Its superolateral surface is articular and participates, with the olecranon, in forming  the  trochlear  notch.  The  lateral  surface  is marked by the radial notch for articulation with the head of the radius.
+Just inferior to the radial notch is a fossa that allows the radial tuberosity to change position during pronation and supination. The posterior margin of this fossa is broadened to form the supinator crest. The anterior surface of the coronoid process is triangular, with the apex directed dis-tally, and has a number of roughenings for muscle attach-ment. The largest of these roughenings, the tuberosity of the ulna, is at the apex of the anterior surface and is the
+attachment site for the brachialis muscle.	741
+Upper Limb
+
+
+
+
+Humerus Head
+
+Neck	Radial tuberosity
+
+
+
+Lateral epicondyle
+
+Capitulum
+
+Medial epicondyle
+
+Trochlea
+
+
+
+Head of radius
+
+Oblique line
+
+
+
+
+Lateral	Medial
+
+Radius	Ulna A                                                                               B
+
+Fig. 7.62  A. Anterior view of the proximal end of the radius. B. Radiograph of the elbow joint (anteroposterior view).
+
+
+
+
+
+
+
+
+Trochlear Olecranon	notch
+
+
+Roughening for triceps attachment
+
+Roughening for anconeus
+
+
+
+
+
+
+
+Radial notch
+Coronoid process
+
+
+
+
+
+Coronoid process
+
+Subcutaneous surface
+
+
+
+Supinator crest
+
+
+Supinator crest
+
+
+Tuberosity of ulna
+
+
+
+
+
+
+
+A	Lateral view	Anterior view	Medial view	Posterior view
+
+742	Fig. 7.63  A. Lateral, anterior, medial, and posterior views of the proximal end of the ulna.
+Regional Anatomy  •  Arm	7
+
+
+Radial tuberosity	Capitulum	Humerus	Transverse humeral ligament
+
+
+
+
+Long head of biceps brachii muscle
+
+Short head of biceps brachii muscle
+
+
+
+
+
+Coracobrachialis muscle
+
+
+Brachialis muscle
+
+
+
+
+
+B
+
+Coronoid process	Trochlear notch	Olecranon	Bicipital aponeurosis (cut)
+
+
+Fig. 7.63, cont’d  B. Radiograph of the elbow joint (lateral view).
+
+
+Muscles
+The  anterior  compartment  of  the  arm  contains  three muscles—the  coracobrachialis,  brachialis,  and  biceps brachii muscles—which are innervated predominantly by the musculocutaneous nerve.
+The posterior compartment contains one muscle—the triceps brachii muscle—which is innervated by the radial nerve.
+
+Coracobrachialis
+The coracobrachialis muscle extends from the tip of the coracoid process of the scapula to the medial side of the midshaft of  the humerus (Fig. 7.64 and Table 7.8). It passes through the axilla and is penetrated and innervated by the musculocutaneous nerve.
+The coracobrachialis muscle flexes the arm.
+
+Biceps brachii
+The biceps brachii muscle has two heads:
+
+Tuberosity of ulna
+
+
+
+Radial tuberosity
+
+
+Fig. 7.64  Coracobrachialis, biceps brachii, and brachialis muscles.
+
+
+
+
+The tendon of the long head passes through the gleno-humeral joint superior to the head of  the humerus and then passes through the intertubercular sulcus and enters the arm. In the arm, the tendon joins with its muscle belly and, together with the muscle belly of  the short head, overlies the brachialis muscle.
+The long and short heads converge to form a single tendon, which inserts onto the radial tuberosity.
+As the tendon enters the forearm, a flat sheet of connec-tive tissue (the bicipital aponeurosis) fans out from the medial side of the tendon to blend with deep fascia covering the anterior compartment of the forearm.
+The biceps brachii muscle is a powerful flexor of  the forearm at the elbow joint; it is also the most powerful
+
+
+
+■     The short head of the muscle originates from the cora-coid process in conjunction with the coracobrachialis.
+■     The long head originates as a tendon from the supragle-noid tubercle of the scapula (Fig. 7.64 and Table 7.8).
+
+supinator of the forearm when the elbow joint is flexed. Because the two heads of the biceps brachii muscle cross the glenohumeral joint, the muscle can also flex the gleno-
+humeral joint.	743
+Upper Limb
+
+
+Table 7.8    Muscles of the anterior compartment of the arm (spinal segments in bold are the major segments innervating the muscle)
+
+
+Muscle Coracobrachialis
+
+
+Biceps brachii
+
+
+
+Brachialis
+
+Origin
+Apex of coracoid process
+
+
+Long head—supraglenoid tubercle of scapula; short head—apex of coracoid process
+Anterior aspect of humerus (medial and lateral surfaces) and adjacent intermuscular septae
+
+Insertion
+Linear roughening on midshaft of humerus on medial side
+Radial tuberosity
+
+
+
+Tuberosity of the ulna
+
+Innervation
+Musculocutaneous nerve (C5, C6, C7)
+
+Musculocutaneous nerve (C5, C6)
+
+
+Musculocutaneous nerve (C5, C6); small contribution by the radial nerve (C7) to lateral part of muscle
+
+Function
+Flexor of the arm at the glenohumeral joint
+
+Powerful flexor of the forearm at the elbow joint and supinator of the forearm; accessory flexor of the arm at the glenohumeral joint
+Powerful flexor of the forearm at the elbow joint
+
+
+
+The biceps brachii muscle is innervated by the muscu-locutaneous nerve. A tap on the tendon of  the biceps brachii at the elbow is used to test predominantly spinal cord segment C6.
+
+
+In the clinic
+
+Rupture of biceps tendon
+It is relatively unusual for muscles and their tendons to rupture in the upper limb; however, the tendon that most commonly ruptures is the tendon of the long head of the biceps brachii muscle. In isolation, this has relatively little effect on the upper limb, but it does produce a characteristic deformity—on flexing the elbow, there is an extremely prominent bulge of the muscle belly as its unrestrained fibers contract—the “Popeye” sign.
+Distal biceps tendon rupture also occurs. It is important to determine the site of the rupture, whether it’s at the musculotendinous junction, midtendon, or at the insertion because this will determine the surgical approach for repair.
+
+
+
+
+
+
+
+
+
+
+Lateral head of triceps brachii
+
+Radial groove of humerus
+
+Long head of triceps brachii
+
+Medial head of triceps brachii
+
+
+
+Brachialis
+The brachialis muscle originates from the distal half of the anterior aspect of the humerus and from adjacent parts of the intermuscular septa, particularly on the medial side (Fig. 7.64 and Table 7.8). It lies beneath the biceps brachii muscle, is flattened dorsoventrally, and converges to form a tendon, which attaches to the tuberosity of the ulna.
+The brachialis muscle flexes the forearm at the elbow joint.
+Innervation of the brachialis muscle is predominantly by the musculocutaneous nerve. A small component of the lateral part is innervated by the radial nerve.
+
+Posterior compartment
+The only muscle of the posterior compartment of the arm is the triceps brachii muscle (Fig. 7.65 and Table 7.9).
+744	The triceps brachii muscle has three heads:
+
+
+Lateral head of triceps brachii
+
+
+
+Olecranon
+
+
+
+
+
+
+
+Fig. 7.65  Triceps muscle.
+Regional Anatomy  •  Arm	7
+
+
+Table 7.9    Muscle of the posterior compartment of the arm (spinal segment indicated in bold is the major segment innervating the muscle)
+
+
+Muscle
+Triceps brachii
+
+Origin
+Long head—infraglenoid tubercle of scapula; medial head—posterior surface of humerus; lateral head—posterior surface of humerus
+
+Insertion
+Olecranon
+
+Innervation
+Radial nerve (C6, C7, C8)
+
+Function
+Extension of the forearm at the elbow joint; long head can also extend and adduct the arm at the shoulder joint
+
+
+
+
+■     The long head originates from the infraglenoid tubercle of the scapula.
+■     The medial head originates from the extensive area on the posterior surface of the shaft of the humerus inferior to the radial groove.
+■     The lateral head originates from a linear roughening superior to the radial groove of the humerus.
+
+The three heads converge to form a large tendon, which
+
+
+compartment  of  the  arm  (Fig.  7.66A,B).  It  enters  the posterior compartment with the radial nerve and together they pass through the triangular interval, which is formed by the shaft of  the humerus, the inferior margin of  the teres major muscle, and the lateral margin of the long head of  the triceps muscle. They then pass along the radial groove on the posterior surface of the humerus deep to the lateral head of the triceps brachii muscle.
+Branches of the profunda brachii artery supply adjacent
+
+
+
+inserts on the superior surface of  the olecranon of  the ulna.
+The triceps brachii muscle extends the forearm at the elbow joint.
+Innervation of the triceps brachii is by branches of the radial nerve. A tap on the tendon of the triceps brachii tests predominantly spinal cord segment C7.
+
+Arteries and veins Brachial artery
+The major artery of the arm, the brachial artery, is found in the anterior compartment (Fig. 7.66A). Beginning as a continuation of the axillary artery at the lower border of the teres major muscle, it terminates just distal to the elbow joint where it divides into the radial and ulnar arteries.
+In the proximal arm, the brachial artery lies on the medial side. In the distal arm, it moves laterally to assume a position midway between the lateral epicondyle and the medial epicondyle of the humerus. It crosses anteriorly to the elbow joint where it lies immediately medial to the tendon of the biceps brachii muscle. The brachial artery is palpable along its length. In proximal regions, the brachial artery can be compressed against the medial side of the humerus.
+Branches of the brachial artery in the arm include those to adjacent muscles and two ulnar collateral vessels, which contribute to a network of arteries around the elbow joint (Fig. 7.66B). Additional branches are the profunda brachii artery and nutrient arteries to the humerus, which pass through a foramen in the anteromedial surface of  the humeral shaft.
+
+Profunda brachii artery
+The  profunda  brachii  artery,  the  largest  branch  of the brachial artery, passes into and supplies the posterior
+
+muscles and anastomose with the posterior circumflex humeral artery. The artery terminates as two collateral vessels, which contribute to an anastomotic network of arteries around the elbow joint (Fig. 7.66B).
+
+
+
+
+In the clinic
+
+Blood pressure measurement
+Blood pressure measurement is an extremely important physiological parameter. High blood pressure (hypertension) requires treatment to prevent long-term complications such as stroke. Low blood pressure may be caused by extreme blood loss, widespread infection, or poor cardiac output (e.g., after myocardial infarction). Accurate measurement of blood pressure is essential.
+Most clinicians use a sphygmomanometer and a stethoscope. The sphygmomanometer is a device that inflates a cuff around the midportion of the arm to compress the brachial artery against the humerus. The cuff is inflated so it exceeds the systolic blood pressure (greater than 120 mm Hg). The clinician places a stethoscope over the brachial artery in the cubital fossa and listens (auscultates) for the pulse. As the pressure in the arm cuff of the sphygmomanometer is reduced just below the level of the systolic blood pressure, the pulse becomes audible as a regular thumping sound. As the pressure in the sphygmomanometer continues to drop, the regular thumping sound becomes clearer. When the pressure in the sphygmomanometer is less than that of the diastolic blood pressure, the audible thumping sound becomes inaudible. Using the simple scale on the sphygmomanometer, the patient’s blood pressure can be determined. The normal range is 90–120/60–80 mm Hg
+(systolic blood pressure/diastolic blood pressure).	745
+Upper Limb
+
+
+Subclavian artery
+
+
+Axillary artery
+
+
+
+
+
+
+
+Coracobrachialis
+
+
+Teres major
+
+
+Profunda brachii artery
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Brachial artery
+
+
+
+
+
+Radial artery	Bicipital aponeurosis
+
+Ulnar artery
+
+
+
+A
+
+Fig. 7.66  Brachial artery. A. In context.
+
+
+
+
+
+
+
+
+
+746
+Regional Anatomy  •  Arm	7
+
+
+
+Axillary artery
+
+
+
+
+
+Anterior circumflex humeral artery
+
+Posterior circumflex humeral artery
+
+
+
+
+
+
+
+
+Profunda brachii artery (in radial groove)
+
+Humeral nutrient artery
+
+Brachial artery
+
+
+
+Superior ulnar collateral artery Radial collateral artery
+
+Middle collateral artery
+
+
+Inferior ulnar collateral artery
+
+
+Recurrent interosseous artery
+
+
+
+Radial recurrent artery
+
+
+Radial artery
+
+Posterior interosseous artery
+
+
+B
+
+
+Anterior ulnar recurrent artery
+
+Posterior ulnar recurrent artery
+
+Common interosseous artery
+
+Anterior interosseous artery
+
+Ulnar artery
+
+
+Fig. 7.66, cont’d  Brachial artery. B. Branches.
+
+
+
+
+
+
+
+747
+Upper Limb
+
+
+
+
+Veins
+Paired brachial veins pass along the medial and lateral sides  of  the  brachial  artery,  receiving  tributaries  that accompany branches of the artery (Fig. 7.67).
+In addition to these deep veins, two large subcutaneous veins, the basilic vein and the cephalic vein, are located in the arm.
+
+The basilic vein passes vertically in the distal half of the arm, penetrates deep fascia to assume a position medial to the brachial artery, and then becomes the axillary vein at the lower border of the teres major muscle. The brachial veins join the basilic, or axillary, vein.
+The cephalic vein passes superiorly on the anterolateral aspect of  the arm and through the anterior wall of  the axilla to reach the axillary vein.
+
+
+
+
+
+
+
+
+Axillary vein
+
+
+
+
+
+Coracobrachialis
+
+
+
+Inferior margin of teres major
+
+
+
+
+Basilic vein penetrates deep fascia
+
+
+Paired brachial veins
+
+
+
+Cephalic vein
+
+
+Biceps brachii
+
+Basilic vein
+
+
+Brachialis
+
+
+Basilic vein (subcutaneous superficial vein)
+Deep veins accompanying arteries
+
+
+
+
+
+
+748	Fig. 7.67  Veins of the arm.
+Regional Anatomy  •  Arm	7
+
+
+
+
+Nerves Musculocutaneous nerve
+The musculocutaneous nerve leaves the axilla and enters
+
+penetrates deep fascia, and continues as the lateral cuta-neous nerve of the forearm.
+The musculocutaneous nerve provides:
+
+
+
+the arm by passing through the coracobrachialis muscle (Fig. 7.68). It passes diagonally down the arm in the plane between the biceps brachii and brachialis muscles. After giving rise to motor branches in the arm, it emerges later-ally to the tendon of the biceps brachii muscle at the elbow,
+
+■     motor innervation to all muscles in the anterior com-partment of the arm, and
+■     sensory innervation to skin on the lateral surface of the forearm.
+
+
+
+
+
+Lateral cord
+
+
+
+
+
+
+Musculocutaneous nerve
+
+
+
+
+
+
+
+
+
+
+
+
+Musculocutaneous nerve
+
+Medial cord
+
+
+
+
+
+
+
+
+
+
+
+
+Median nerve
+
+
+
+
+Ulnar nerve
+
+Medial intermuscular septum
+
+Radial nerve
+
+
+
+
+Lateral cutaneous
+nerve of forearm	Medial epicondyle
+
+
+
+
+
+
+
+
+
+Fig. 7.68  Musculocutaneous, median, and ulnar nerves in the arm.	749
+Upper Limb
+
+
+
+
+Median nerve
+The median nerve enters the arm from the axilla at the inferior margin of  the teres major muscle (Fig. 7.68). It passes vertically down the medial side of the arm in the anterior compartment and is related to the brachial artery throughout its course:
+
+margin of the teres major muscle (Fig. 7.69). As it enters the arm, it lies posterior to the brachial artery. Accompa-nied by the profunda brachii artery, the radial nerve enters the posterior compartment of the arm by passing through the triangular interval.
+As the radial nerve passes diagonally, from medial to lateral, through the posterior compartment, it lies in the
+
+
+■     In proximal regions, the median nerve is immediately lateral to the brachial artery.
+■     In more distal regions, the median nerve crosses to the medial side of the brachial artery and lies anterior to the elbow joint.
+
+The median nerve has no major branches in the arm,
+
+radial groove directly on bone. On the lateral side of the arm, it passes anteriorly through the lateral intermuscular septum and enters the anterior compartment where it lies between the brachialis muscle and a muscle of the posterior compartment of the forearm—the brachioradialis muscle, which attaches to the lateral supraepicondylar ridge of the humerus. The radial nerve enters the forearm anterior to the lateral epicondyle of  the humerus, just deep to the
+
+
+
+but a branch to one of  the muscles of  the forearm, the pronator teres muscle, may originate from the nerve imme-diately proximal to the elbow joint.
+
+brachioradialis muscle.
+In the arm, the radial nerve has muscular and cutane-ous branches (Fig. 7.69).
+
+
+
+Ulnar nerve
+The ulnar nerve enters the arm with the median nerve and axillary artery (Fig. 7.68). It passes through proximal regions medial to the axillary artery. In the middle of the arm, the ulnar nerve penetrates the medial intermus-cular septum and enters the posterior compartment where it lies anterior to the medial head of  the triceps brachii muscle. It passes posterior to the medial epicondyle of the humerus and then into the anterior compartment of the forearm.
+The ulnar nerve has no major branches in the arm.
+
+Radial nerve
+The radial nerve originates from the posterior cord of the brachial plexus and enters the arm by crossing the inferior
+
+
+■     Muscular branches include those to the triceps brachii, brachioradialis,  and  extensor  carpi  radialis  longus muscles. In addition, the radial nerve contributes to the innervation of the lateral part of the brachialis muscle. One of the branches to the medial head of the triceps brachii muscle arises before the radial nerve’s entrance into the posterior compartment and passes vertically down the arm in association with the ulnar nerve.
+■     Cutaneous branches of the radial nerve that originate in the posterior compartment of the arm are the infe-rior lateral cutaneous nerve of  the arm and the posterior cutaneous nerve of the forearm, both of which penetrate through the lateral head of the triceps brachii muscle and the overlying deep fascia to become subcutaneous.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+750
+Regional Anatomy  •  Arm	7
+
+
+
+
+
+
+
+
+
+Triangular interval
+
+
+
+
+Profunda brachii artery
+
+
+
+
+
+Radial nerve (in radial groove)
+
+
+
+
+
+Inferior lateral cutaneous nerve of arm
+
+
+
+
+
+
+
+
+
+Branch to medial head of triceps brachii	Posterior cutaneous nerve of forearm
+
+
+Medial epicondyle
+
+Ulnar nerve
+
+
+
+
+
+
+
+
+Fig. 7.69  Radial nerve in the arm.
+
+
+
+
+
+
+
+
+751
+Upper Limb
+
+
+
+In the clinic
+
+Radial nerve injury in the arm
+The radial nerve is tightly bound with the profunda brachii artery between the medial and lateral heads of the triceps brachii muscle in the radial groove. If the humerus is fractured, the radial nerve may become stretched or transected in this region, leading to permanent damage and loss of function. This injury is typical (Fig. 7.70) and the nerve should always be tested when a fracture of the midshaft of the humerus is suspected. The patient’s symptoms usually include wrist drop (due to denervation of the extensor muscles) and sensory changes over the dorsum of the hand.
+
+Humerus
+
+In the clinic
+
+Median nerve injury in the arm
+In the arm and forearm the median nerve is usually not injured by trauma because of its relatively deep position. The commonest neurological problem associated with the median nerve is compression beneath the flexor retinaculum at the wrist (carpal tunnel syndrome).
+On very rare occasions, a fibrous band may arise from the anterior aspect of the humerus beneath which the median nerve passes. This is an embryological remnant of the coracobrachialis muscle and is sometimes called the ligament of Struthers; occasionally, it may calcify. This band can compress the median nerve, resulting in weakness of the flexor muscles in the forearm and the thenar muscles. Nerve conduction studies will demonstrate the site of nerve compression.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 7.70  Radiograph of the humerus demonstrating a midshaft fracture, which may disrupt the radial nerve.
+
+
+
+752
+Regional Anatomy  •  Elbow Joint	7
+
+
+
+ELBOW JOINT
+
+The elbow joint is a complex joint involving three separate articulations, which share a common synovial cavity (Fig. 7.71).
+
+primarily involved with hinge-like flexion and extension of the forearm on the arm and, together, are the princi-pal articulations of the elbow joint.
+■     The joint between the head of the radius and the radial notch of  the ulna, the proximal radio-ulnar joint, is involved with pronation and supination of the forearm.
+
+
+
+■     The joints between the trochlear notch of  the ulna and the trochlea of the humerus and between the head of  the radius and the capitulum of  the humerus are
+
+
+The articular surfaces of  the bones are covered with hyaline cartilage.
+
+
+
+
+
+
+
+Trochlea
+
+
+
+
+Capitulum
+
+
+
+Head (of radius)
+
+Trochlear notch (of ulna)
+
+
+Radial notch (of ulna)
+
+
+
+Humerus
+
+
+A
+
+
+
+
+
+Capitulum	Trochlea
+
+
+Head of Flexion	radius
+
+
+Extension
+
+
+B	Pronation
+
+Supination
+Radius	Ulna
+C	D
+
+Fig. 7.71  Components and movements of the elbow joint. A. Bones and joint surfaces. B. Flexion and extension. C. Pronation and supination.
+D. Radiograph of a normal elbow joint (anteroposterior view).	753
+Upper Limb
+
+
+
+The synovial membrane originates from the edges of the articular cartilage and lines the radial fossa, the coronoid fossa, the olecranon fossa, the deep surface of  the joint capsule, and the medial surface of the trochlea (Fig. 7.72). The synovial membrane is separated from the fibrous membrane of the joint capsule by pads of fat in regions overlying the coronoid fossa, the olecranon fossa, and the radial fossa. These fat pads accommodate the related bony
+
+
+
+
+
+
+Fat pads
+
+processes  during  extension  and  flexion  of  the  elbow.
+
+Attachments of the brachialis and triceps brachii muscles to the joint capsule overlying these regions pull the attached fat pads out of the way when the adjacent bony processes are moved into the fossae.
+The fibrous membrane of the joint capsule overlies the synovial membrane, encloses the joint, and attaches to the medial epicondyle and the margins of the olecranon, coro-noid, and radial fossae of the humerus (Fig. 7.73). It also attaches to the coronoid process and olecranon of  the ulna. On the lateral side, the free inferior margin of the joint capsule passes around the neck of the radius from an anterior attachment to the coronoid process of the ulna to a posterior attachment to the base of the olecranon.
+The fibrous membrane of the joint capsule is thickened
+
+
+
+
+Anular ligament of radius
+
+
+Sacciform recess of synovial membrane
+
+
+Synovial membrane
+
+medially and laterally to form collateral ligaments, which
+Fig. 7.72  Synovial membrane of elbow joint (anterior view).
+
+
+
+
+Radial collateral ligament	Humerus	Medial epicondyle
+
+
+
+
+
+
+
+Radial collateral ligament
+
+Anular ligament of radius
+
+
+
+
+Ulnar collateral ligament
+
+
+
+Sacciform recess of synovial membrane
+
+
+
+B
+
+
+A	Head of radius	Ulna
+
+Ulnar collateral ligament
+
+
+Fig. 7.73  Elbow joint. A. Joint capsule and ligaments of the right elbow joint. B. Magnetic resonance image of the elbow joint in the coronal 754	plane.
+Regional Anatomy  •  Elbow Joint	7
+
+
+support the flexion and extension movements of the elbow       articulate with the sides of  the radial head are lined by joint (Fig. 7.73).                                                                            cartilage.  A  pocket  of  synovial  membrane  (sacciform
+
+In addition, the external surface of the joint capsule is reinforced laterally where it cuffs the head of the radius with a strong anular ligament of the radius. Although this ligament blends with the fibrous membrane of  the joint capsule in most regions, they are separate posteriorly. The anular ligament of  the radius also blends with the radial collateral ligament.
+The anular ligament of  the radius and related joint capsule allow the radial head to slide against the radial notch of the ulna and pivot on the capitulum during pro-nation and supination of the forearm.
+The deep surface of the fibrous membrane of the joint capsule and the related anular ligament of the radius that
+
+
+
+
+In the clinic
+
+Supracondylar fracture of the humerus
+Elbow injuries in children may result in a transverse fracture of the distal end of the humerus, above the level of the epicondyles. This fracture is termed a supracondylar fracture. The distal fragment and its soft tissues are pulled posteriorly by the triceps muscle. This posterior displacement effectively “bowstrings” the brachial artery over the irregular proximal fracture fragment. In children, this is a relatively devastating injury: the muscles of the anterior compartment of the forearm are rendered ischemic and form severe contractions, significantly reducing the function of the anterior compartment and flexor muscles (Volkmann’s ischemic contracture).
+
+
+
+
+In the clinic
+
+Pulled elbow
+Pulled elbow is a disorder that typically occurs in children under 5 years of age. It is commonly caused by a sharp pull of the child’s hand, usually when the child is pulled up a curb. The not-yet-developed head of the radius and the laxity of the anular ligament of the radius allow the head to sublux from this cuff of tissue. Pulled elbow is extremely painful, but can be treated easily by simple supination and compression of the elbow joint by the clinician. When the radial head is relocated the pain subsides immediately and the child can continue with normal activity.
+
+recess) protrudes from the inferior free margin of the joint capsule and facilitates rotation of the radial head during pronation and supination.
+Vascular supply to the elbow joint is through an anas-tomotic network of  vessels derived from collateral and recurrent  branches  of  the  brachial,  profunda  brachii, radial, and ulnar arteries.
+The elbow joint is innervated predominantly by branches of the radial and musculocutaneous nerves, but there may be some innervation by branches of the ulnar and median nerves.
+
+
+
+
+
+
+In the clinic
+
+Fracture of the olecranon
+Fractures of the olecranon can result from a direct blow to the olecranon or from a fall onto an outstretched hand (Fig. 7.74). The triceps inserts into the olecranon and injuries can cause avulsion of the muscle.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Olecranon
+
+Fig. 7.74  Radiograph of an elbow showing a fracture of the olecranon and involving the insertion of the triceps brachii muscle.
+
+
+
+755
+Upper Limb
+
+
+
+In the clinic
+
+Developmental changes in the elbow joint
+The elbow joint can be injured in many ways; the types of injuries are age dependent. When a fracture or soft tissue trauma is suspected, a plain lateral and an anteroposterior radiograph are obtained. In an adult it is usually not difficult to interpret the radiograph, but in children additional factors require interpretation.
+As the elbow develops in children, numerous secondary ossification centers appear before and around puberty. It is easy to mistakenly interpret these as fractures. In addition, it is also possible for the epiphyses and apophyses to be “pulled off” or disrupted. Therefore, when interpreting a child’s radiograph of the elbow, the physician must know
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+C
+
+
+
+the child’s age (Fig. 7.75). Fusion occurs at around the time of puberty. An understanding of the normal epiphyses and apophyses and their normal relationship to the bones will secure a correct diagnosis. The approximate ages of appearance of the secondary ossification centers around the elbow joint are:
+
+■     capitulum—1 year,
+■     head (of radius)—5 years,
+■     medial epicondyle—5 years, ■     trochlea—11 years,
+■     olecranon—12 years, and
+■     lateral epicondyle—13 years.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+B
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+D
+
+
+Fig. 7.75  Radiographs of elbow joint development. A. At age 2 years. B. At age 5 years. C. At age 5–6 years. D. At age 12 years.
+
+
+
+
+756
+Regional Anatomy  •  Elbow Joint	7
+
+
+
+In the clinic
+
+Fracture of the head of the radius
+A fracture of the head of the radius is a common injury and can cause appreciable morbidity. It is one of the typical injuries that occur with a fall on the outstretched hand. On falling, the force is transmitted to the radial head, which fractures. These fractures typically result in loss of full extension, and potential surgical reconstruction may require long periods of physiotherapy to obtain a full range of movement at the elbow joint.
+A lateral radiograph of a fracture of the head of the radius typically demonstrates the secondary phenomenon of this
+
+
+
+
+
+
+In the clinic
+
+“Tennis” and “golfer’s” elbow (epicondylitis)
+It is not uncommon for people who are involved in sports such as golf and tennis to develop an overuse strain of the origins of the flexor and extensor muscles of the forearm. The pain is typically around the epicondyles and usually resolves after rest and physical therapy. It may also be treated with injection of the patient’s own plasma, rich in platelets, into the tendon to promote tendon healing and repair. If pain and inflammation persist, surgical division of the extensor or flexor origin from the bone may be necessary. Typically, in tennis players this pain occurs on the lateral epicondyle and common extensor origin (tennis elbow), whereas in golfers it occurs on the medial epicondyle and common flexor origin.
+
+
+
+injury. When the bone is fractured, fluid fills the synovial cavity, elevating the small pad of fat within the coronoid and olecranon fossae. These fat pads appear as areas of lucency on the lateral radiograph—the “fat pad” sign. This radiological finding is useful because fracture of the head of the radius is not always clearly visible. If there is an appropriate clinical history, tenderness around the head of the radius, and a positive fat pad sign, a fracture can be inferred clinically even if no fracture can be identified on the radiograph, and appropriate treatment can be instituted.
+
+
+
+
+
+
+
+In the clinic
+
+Elbow arthritis
+Osteoarthritis is extremely common and is usually most severe in the dominant limb. From time to time an arthritic elbow may undergo such degenerative change that small bone fragments appear in the articular cavity. Given the relatively small joint space, these fragments can result in an appreciable reduction in flexion and extension, and typically lodge within the olecranon and coronoid fossae.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+757
+Upper Limb
+
+
+
+In the clinic
+
+Ulnar nerve injury at the elbow
+Posterior to the medial epicondyle of the humerus the ulnar nerve is bound in a fibro-osseous tunnel (the cubital tunnel) by a retinaculum. Older patients may develop degenerative changes within this tunnel, which compresses the ulnar nerve when flexed. The repeated action of flexion and extension of the elbow may cause local nerve damage, resulting in impaired function of the ulnar nerve. Accessory muscles and localized neuritis in this region secondary to direct trauma may also produce ulnar nerve damage (Fig. 7.76).
+
+CUBITAL FOSSA
+
+The cubital fossa is an important area of transition between the arm and the forearm. It is located anterior to the elbow joint and is a triangular depression formed between two forearm muscles:
+
+■     the brachioradialis muscle originating from the lateral supra-epicondylar ridge of the humerus, and
+■     the pronator teres muscle originating from the medial epicondyle of the humerus (Fig. 7.77A).
+
+The base of the triangle is an imaginary horizontal line between the medial and lateral epicondyles. The bed or floor of the fossa is formed mainly by the brachialis muscle. The major contents of the cubital fossa, from lateral to
+medial, are:
+
+
+■     the tendon of the biceps brachii muscle, ■     the brachial artery, and
+■     the median nerve (Fig. 7.77B).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Ulnar nerve
+
+Fig. 7.76  MRI of right elbow showing swelling of the ulnar nerve in the cubital tunnel posterior to the medial epicondyle, consistent with nerve compression.
+
+The brachial artery normally bifurcates into the radial and ulnar arteries in the apex of  the fossa (Fig. 7.77B), although this bifurcation may occur much higher in the arm, even in the axilla. When taking a blood pressure reading from a patient, the clinician places the stethoscope over the brachial artery in the cubital fossa.
+The median nerve lies immediately medial to the bra-chial artery and leaves the fossa by passing between the ulnar and humeral heads of  the pronator teres muscle (Fig. 7.77C).
+The brachial artery and the median nerve are covered and protected anteriorly in the distal part of the cubital fossa by the bicipital aponeurosis (Fig. 7.77B). This flat connective tissue membrane passes between the medial side of the tendon of the biceps brachii muscle and deep
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+758
+Regional Anatomy  •  Cubital Fossa	7
+
+
+
+Triceps brachii
+
+
+
+Medial intermuscular septum
+
+Artery (brachial)
+
+
+
+Brachialis
+Biceps brachii Cubital fossa
+
+
+Nerve (median)
+
+
+
+
+
+Line between lateral and medial epicondyles
+
+
+
+
+Brachioradialis
+
+
+
+
+A
+
+
+Pronator teres
+
+Tendon (biceps brachii)
+
+Forearm flexors
+Radial artery
+
+
+Ulnar artery
+
+
+
+B
+
+
+
+
+Bicipital aponeurosis
+
+
+
+Forearm extensors
+
+
+
+Ulnar nerve
+
+Radial nerve
+
+
+Lateral epicondyle
+
+Tendon (biceps)
+Artery (brachial)
+Nerve (median)
+
+Ulnar nerve
+
+
+Medial epicondyle
+
+
+Radial nerve
+Median nerve
+
+Ulnar nerve
+
+Basilic vein
+
+Medial cutaneous nerve of forearm
+
+
+
+Radial nerve
+
+
+
+Brachioradialis (pulled back)
+
+
+Deep branch of radial nerve
+
+Musculocutaneous nerve
+
+Pronator teres (humeral head)
+
+
+Lateral cutaneous nerve of forearm
+
+Pronator teres (ulnar head)
+
+Ulnar artery
+
+Median nerve
+
+
+
+
+
+
+
+Median cubital vein
+
+
+Supinator
+
+
+Radial artery
+
+
+
+C	Superficial branch of radial nerve	D	Cephalic vein	Basilic vein
+
+Fig. 7.77  Cubital fossa. A. Margins. B. Contents. C. Position of the radial nerve. D. Superficial structures.
+759
+Upper Limb
+
+
+
+fascia of  the forearm. The sharp medial margin of  the bicipital aponeurosis can often be felt.
+The radial nerve lies just under the lip of the brachiora-dialis muscle, which forms the lateral margin of the fossa
+
+The ulnar nerve does not pass through the cubital fossa. Instead, it passes posterior to the medial epicondyle.
+The roof  of  the cubital fossa is formed by superficial fascia and skin. The most important structure within the
+
+(Fig. 7.77C). In this position, the radial nerve divides into       roof   is  the  median  cubital  vein  (Fig.  7.77D),  which superficial and deep branches:                                                     passes  diagonally  across  the  roof   and  connects  the
+
+
+■     The superficial branch continues into the forearm just deep to the brachioradialis muscle.
+■     The deep branch passes between the two heads of the supinator muscle (see pp. 778–780 and Fig. 7.92) to access the posterior compartment of the forearm.
+
+cephalic vein on the lateral side of the upper limb with the basilic vein on the medial side. The bicipital aponeurosis separates the median cubital vein from the brachial artery and median nerve. Other structures within the roof  are cutaneous  nerves—the  medial  cutaneous  and  lateral cutaneous nerves of the forearm.
+
+
+
+
+In the clinic
+
+Construction of a dialysis fistula
+Many patients throughout the world require renal dialysis for kidney failure. The patient’s blood is filtered and cleaned by the dialysis machine. Blood therefore has to be taken from patients into the filtering device and then returned to them. This process of dialysis occurs over many hours and requires considerable flow rates of 250–500 mL per minute. To enable such large volumes of blood to be removed from and returned to the body, the blood is taken from vessels that have a high flow. As no veins in the peripheral limbs have such high flow, a surgical procedure is necessary to create such a system. In most patients, the radial artery is anastomosed (joined) to the cephalic vein (Fig. 7.78) at the wrist, or the brachial artery is anastomosed to the cephalic vein at the elbow. Some surgeons place an arterial graft between these vessels.
+After six weeks, the veins increase in size in response to their arterial blood flow and are amenable to direct cannulation or dialysis.
+
+
+
+Ulnar artery	Fistula	Radial artery
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+Radial artery	Draining vein
+
+Fig. 7.78  Digital subtraction angiograms of forearm demonstrating a surgically created radiocephalic fistula. A. Anteroposterior view. B. Lateral view.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+760
+Regional Anatomy  •  Forearm	7
+
+
+
+FOREARM
+
+The forearm is the part of  the upper limb that extends between the elbow joint and the wrist joint. Proximally, most major structures pass between the arm and forearm through, or in relation to, the cubital fossa, which is ante-rior to the elbow joint (Fig. 7.79). The exception is the
+
+ulnar nerve, which passes posterior to the medial epicon-dyle of the humerus.
+Distally, structures pass between the forearm and the hand through, or anterior to, the carpal tunnel (Fig. 7.79). The major exception is the radial artery, which passes dorsally around the wrist to enter the hand posteriorly.
+
+
+
+
+Arm
+
+Biceps tendon Brachial artery Median nerve
+
+Elbow joint
+
+
+Cubital fossa
+
+
+Forearm
+
+
+Radius
+
+Ulna
+Wrist joint	Median nerve Long flexor tendons of digits
+
+
+
+Carpal tunnel Hand
+
+
+A
+
+Lateral intermuscular septum
+
+Deep fascia	Anterior compartment
+
+
+
+
+
+Radius
+Ulna Posterior
+compartment
+
+
+B	Interosseous membrane
+
+Fig. 7.79  Forearm. A. Proximal and distal relationships of the forearm. B. Transverse section through the middle of the forearm.
+
+761
+Upper Limb
+
+
+
+The bone framework of  the forearm consists of  two parallel bones, the radius and the ulna (Figs. 7.79 and 7.80B). The radius is lateral in position and is small proxi-mally, where it articulates with the humerus, and large
+
+As in the arm, the forearm is divided into anterior and posterior compartments (Fig. 7.79). In the forearm, these compartments are separated by:
+
+
+
+distally, where it forms the wrist joint with the carpal bones of the hand.
+The ulna is medial in the forearm, and its proximal
+
+■     a lateral intermuscular septum, which passes from the anterior border of the radius to deep fascia surrounding the limb;
+
+and distal dimensions are the reverse of  those for the	■     an   interosseous   membrane,   which   links   adjacent
+
+radius: the ulna is large proximally and small distally. Proximal and distal joints between the radius and the ulna allow the distal end of the radius to swing over the adjacent end of the ulna, resulting in pronation and supination of the hand.
+
+borders of  the radius and ulna along most of  their length; and
+■     the attachment of deep fascia along the posterior border of the ulna.
+
+
+Head	Humerus
+Neck	Anterior view
+
+Radial tuberosity
+
+
+
+Roughening for attachment
+of pronator teres
+
+Oblique line
+
+Anterior border
+
+Anterior surface
+
+
+
+Lateral surface
+
+
+Interosseous border
+
+
+Posterior surface
+Posterior border
+Anterior border
+Interosseous border
+
+
+Posterior view
+
+
+
+Ulnar notch
+
+
+Radius
+
+
+
+Radial styloid process
+
+
+
+
+Facet for articulation with scaphoid bone
+A
+
+Dorsal tubercle
+
+Ulna
+
+Distal view
+
+
+Facet for articulation with lunate bone
+
+B
+
+
+762	Fig. 7.80  Radius. A. Shaft and distal end of the right radius. B. Radiograph of the forearm (anteroposterior view).
+Regional Anatomy  •  Forearm	7
+
+
+
+
+Trochlear	Olecranon notch
+Coronoid process
+
+broader distally, where it expands to form the distal end (Fig. 7.80).
+Throughout most of its length, the shaft of the radius is triangular in cross section, with:
+
+
+
+Anterior view Radial notch
+
+Tuberosity of ulna
+
+
+■     three  borders  (anterior,  posterior,  and  interosseous), and
+■     three surfaces (anterior, posterior, and lateral).
+
+
+
+
+
+
+Anterior surface
+
+
+
+
+
+Interosseous border
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Attachment of articular disc
+
+
+
+Anterior surface
+
+Anterior border Interosseous	(rounded) border
+
+Medial surface
+
+Posterior border (sharp)
+Posterior surface
+
+Anterior border
+
+
+Roughening for attachment
+of pronator quadratus
+
+
+
+
+
+
+
+Ulnar styloid process
+
+Distal view
+
+The anterior border begins on the medial side of the bone as a continuation of  the radial tuberosity. In the superior third of the bone, it crosses the shaft diagonally, from medial to lateral, as the oblique line of the radius. The posterior border is distinct only in the middle third of the bone. The interosseous border is sharp and is the attach-ment site for the interosseous membrane, which links the radius to the ulna.
+The anterior and posterior surfaces of  the radius are generally smooth, whereas an oval roughening for the attachment of the pronator teres marks approximately the middle of the lateral surface of the radius.
+Viewed anteriorly, the distal end of the radius is broad and  somewhat  flattened  anteroposteriorly  (Fig.  7.80). Consequently, the radius has expansive anterior and poste-rior surfaces and narrow medial and lateral surfaces. Its anterior surface is smooth and unremarkable, except for the prominent sharp ridge that forms its lateral margin.
+The posterior surface of the radius is characterized by the presence of a large dorsal tubercle, which acts as a pulley for the tendon of one of the extensor muscles of the thumb (extensor pollicis longus). The medial surface is marked by a prominent facet for articulation with the distal end of the ulna (Fig. 7.80). The lateral surface of the radius is diamond shaped and extends distally as a radial styloid process.
+
+
+
+
+Fig. 7.81  Shaft and distal end of right ulna.
+
+
+
+
+
+Muscles in the anterior compartment of the forearm flex the wrist and digits and pronate the hand. Muscles in the posterior compartment extend the wrist and digits and
+
+The distal end of the bone is marked by two facets for articulation  with  two  carpal  bones  (the  scaphoid  and lunate).
+
+Shaft and distal end of ulna
+The shaft of the ulna is broad superiorly where it is con-tinuous with the large proximal end and narrow distally to form a small distal head (Fig. 7.81). Like the radius, the shaft of the ulna is triangular in cross section and has:
+
+
+
+supinate the hand. Major nerves and vessels supply or pass through each compartment.
+
+
+Bones
+Shaft and distal end of radius
+
+
+■     three  borders  (anterior,  posterior,  and  interosseous), and
+■     three surfaces (anterior, posterior, and medial).
+
+The  anterior  border  is  smooth  and  rounded. The
+
+
+
+The shaft of the radius is narrow proximally, where it is continuous with the radial tuberosity and neck, and much
+
+posterior border is sharp and palpable along its entire length. The interosseous border is also sharp and is the	763
+Upper Limb
+
+
+
+attachment site for the interosseous membrane, which joins the ulna to the radius.
+The anterior surface of  the ulna is smooth, except distally where there is a prominent linear roughening for the attachment of  the pronator quadratus muscle. The medial surface is smooth and unremarkable. The poste-rior surface is marked by lines, which separate different regions of muscle attachments to bone.
+The distal end of the ulna is small and characterized by a rounded head and the ulnar styloid process (Fig. 7.81). The anterolateral and distal part of the head is covered by articular cartilage. The ulnar styloid process originates from the posteromedial aspect of  the ulna and projects distally.
+
+
+
+
+
+
+
+
+Anular ligament
+
+
+
+
+Oblique cord
+
+
+
+
+Ulna
+
+
+
+
+In the clinic
+
+Fractures of the radius and ulna
+The radius and ulna are attached to the humerus proximally and the carpal bones distally by a complex series of ligaments. Although the bones are separate, they behave as one. When a severe injury occurs to the forearm it usually involves both bones, resulting in either fracture of both bones or more commonly a fracture of one bone and a dislocation of the other. Commonly, the mechanism of injury and the age of the patient determine which of these are likely to occur.
+There are three classic injuries to the radius and ulna:
+
+
+
+
+
+
+
+
+Radius
+
+
+
+Wrist joint
+
+
+Interosseous membrane
+
+
+
+
+Aperture for anterior interosseous artery
+
+Distal radio-ulnar joint
+
+Articular disc
+
+
+■     Monteggia’s fracture is a fracture of the proximal third of the ulna and an anterior dislocation of the head of the radius at the elbow.
+■     Galeazzi’s fracture is a fracture of the distal third of the radius associated with subluxation (partial dislocation) of the head of the ulna at the wrist joint.
+■     Colles’ fracture is a fracture, and posterior displacement, of the distal end of the radius.
+
+Whenever a fracture of the radius or ulna is demonstrated radiographically, further images of the elbow and wrist should be obtained to exclude dislocations.
+
+
+
+
+
+Joints
+Distal radio-ulnar joint
+The distal radio-ulnar joint occurs between the articular surface of the head of the ulna, with the ulnar notch on the end of  the radius, and with a fibrous articular disc, which separates the radio-ulnar joint from the wrist joint
+764	(Fig. 7.82).
+
+
+Fig. 7.82  Distal radio-ulnar joint and the interosseous membrane.
+Regional Anatomy  •  Forearm	7
+
+
+
+The triangular-shaped articular disc is attached by its apex to a roughened depression on the ulna between the styloid process and the articular surface of the head, and by its base to the angular margin of the radius between the ulnar notch and the articular surface for the carpal bones. The synovial membrane is attached to the margins of the distal radio-ulnar joint and is covered on its external
+surface by a fibrous joint capsule.
+The distal radio-ulnar joint allows the distal end of the radius to move anteromedially over the ulna.
+
+Interosseous membrane
+The interosseous membrane is a thin fibrous sheet that connects the medial and lateral borders of the radius and ulna, respectively (Fig. 7.82). Collagen fibers within the sheet pass predominantly inferiorly from the radius to the ulna.
+The interosseous membrane has a free upper margin, which is situated just inferior to the radial tuberosity, and
+
+posterior compartments. The orientation of fibers in the membrane is also consistent with its role in transferring forces from the radius to the ulna and ultimately, therefore, from the hand to the humerus.
+
+Pronation and supination
+Pronation and supination of  the hand occur entirely in the forearm and involve rotation of the radius at the elbow and movement of the distal end of the radius over the ulna (Fig. 7.83).
+At the elbow, the superior articular surface of the radial head spins on the capitulum while, at the same time, the articular surface on the side of the head slides against the radial notch of the ulna and adjacent areas of the joint capsule and anular ligament of the radius. At the distal radio-ulnar  joint,  the  ulnar  notch  of  the  radius  slides anteriorly over the convex surface of the head of the ulna. During these movements, the bones are held together by:
+
+
+
+a small circular aperture in its distal third. Vessels pass between the anterior and posterior compartments superior to the upper margin and through the inferior aperture.
+
+■     the anular ligament of the radius at the proximal radio-ulnar joint,
+■     the interosseous membrane along the lengths of  the
+
+The   interosseous   membrane   connects   the   radius	radius and ulna, and
+and ulna without restricting pronation and supination	■     the   articular   disc   at   the   distal   radio-ulnar   joint and provides attachment for muscles in the anterior and           (Fig. 7.83).
+
+
+
+
+Biceps brachii
+
+
+
+Supinator
+
+Pronator teres
+
+
+
+
+
+Pronator quadratus
+
+Pronator teres and pronator quadratus contract
+
+
+Supinator and biceps brachii contract
+
+
+
+
+
+
+
+
+Axis of movement
+Supinated	Pronated	Supinated
+
+Fig. 7.83  Pronation and supination.	765
+Upper Limb
+
+
+
+Because the hand articulates predominantly with the	Anconeus radius, the translocation of  the distal end of  the radius
+medially over the ulna moves the hand from the palm-anterior (supinated) position to the palm-posterior (pro-nated) position.
+Two muscles supinate and two muscles pronate the hand (Fig. 7.83).
+
+Muscles involved in pronation and supination
+Biceps brachii.  The biceps brachii muscle, the largest of the four muscles that supinate and pronate the hand, is a powerful supinator as well as a flexor of  the elbow joint. It is most effective as a supinator when the forearm is flexed.
+Supinator.  The  second  of  the  muscles  involved  with supination is the supinator muscle. Located in the poste-rior compartment of  the forearm, it has a broad origin, from the supinator crest of the ulna and the lateral epicon-dyle of the humerus and from ligaments associated with the elbow joint.
+The  supinator  muscle  curves  around  the  posterior surface and the lateral surface of the upper third of the
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Abduction of ulna by anconeus
+during pronation
+
+
+
+radius to attach to the shaft of the radius superior to the oblique line.
+The tendon of the biceps brachii muscle and the supina-tor muscle both become wrapped around the proximal end of the radius when the hand is pronated (Fig. 7.83). When they  contract,  they  unwrap  from  the  bone,  producing supination of the hand.
+Pronator teres and pronator quadratus.  Pronation results from the action of  the pronator teres and pronator quadratus muscles (Fig. 7.83). Both these muscles are in the anterior compartment of the forearm:
+
+
+Axis of movement with abduction of ulna
+
+Fig. 7.84  Abduction of the distal end of the ulna by the anconeus during pronation.
+
+
+
+the lateral epicondyle to the lateral surface of the proximal end of the ulna.
+
+
+
+
+■     The pronator teres runs from the medial epicondyle of the  humerus  to  the  lateral  surface  of  the  radius, approximately midway along the shaft.
+■     The pronator quadratus extends between the anterior surfaces of the distal ends of the radius and ulna.
+
+ANTERIOR COMPARTMENT OF THE FOREARM
+
+Muscles
+Muscles in the anterior (flexor) compartment of the forearm occur in three layers: superficial, intermediate, and deep. Generally, these muscles are associated with:
+
+When these muscles contract, they pull the distal end of the radius over the ulna, resulting in pronation of the hand (Fig. 7.83).
+Anconeus.  In addition to hinge-like flexion and exten-sion at the elbow joint, some abduction of the distal end of the ulna also occurs and maintains the position of the
+
+
+■     movements of the wrist joint,
+■     flexion of the fingers including the thumb, and ■     pronation.
+
+All muscles in the anterior compartment of the forearm
+
+
+
+palm of  the hand over a central axis during pronation (Fig. 7.84). The muscle involved in this movement is the anconeus muscle, which is a triangular muscle in the posterior  compartment  of  the  forearm  that  runs  from
+
+are innervated by the median nerve, except for the flexor carpi ulnaris muscle and the medial half  of  the flexor digitorum profundus muscle, which are innervated by the ulnar nerve.
+
+
+766
+Regional Anatomy  •  Anterior Compartment of the Forearm	7
+
+
+
+
+Superficial layer
+All four muscles in the superficial layer—the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres—have a common origin from the medial epicondyle of the humerus, and, except for the pronator teres, extend distally from the forearm into the hand (Fig. 7.85 and
+Table 7.10).
+
+Flexor carpi ulnaris
+The flexor carpi ulnaris muscle is the most medial of the muscles in the superficial layer of flexors, having a long linear origin from the olecranon and posterior border of the ulna, in addition to an origin from the medial epicon-dyle of the humerus (Fig. 7.85A,B).
+The ulnar nerve enters the anterior compartment of the forearm by passing through the triangular gap between the humeral and ulnar heads of the flexor carpi ulnaris (Fig. 7.85B). The muscle fibers converge on a tendon that passes distally and attaches to the pisiform bone of  the wrist. From this point, force is transferred to the hamate bone of the wrist and to the base of metacarpal V by the pisohamate and pisometacarpal ligaments.
+The flexor carpi ulnaris muscle is a powerful flexor and adductor of the wrist and is innervated by the ulnar nerve (Table 7.10).
+
+Palmaris longus
+The palmaris longus muscle, which is absent in about 15% of the population, lies between the flexor carpi ulnaris and the flexor carpi radialis muscles (Fig. 7.85A). It is a spindle-shaped muscle with a long tendon, which passes into the hand and attaches to the flexor retinaculum and to a thick layer of  deep fascia, the palmar aponeurosis,
+
+which underlies and is attached to the skin of the palm and fingers.
+In addition to its role as an accessory flexor of the wrist joint, the palmaris longus muscle also opposes shearing forces on the skin of the palm during gripping (Table 7.10).
+
+Flexor carpi radialis
+The flexor carpi radialis muscle is lateral to the palmaris longus and has a large and prominent tendon in the distal half of the forearm (Fig. 7.85A and Table 7.10). Unlike the tendon of the flexor carpi ulnaris, which forms the medial margin of the distal forearm, the tendon of the flexor carpi radialis muscle is positioned just lateral to the midline. In this position, the tendon can be easily palpated, making it an important landmark for finding the pulse in the radial artery, which lies immediately lateral to it.
+The tendon of the flexor carpi radialis passes through a compartment formed by bone and fascia on the lateral side of  the anterior surface of  the wrist and attaches to the anterior surfaces of the bases of metacarpals II and III.
+The flexor carpi radialis is a powerful flexor of the wrist and can also abduct the wrist.
+
+Pronator teres
+The pronator teres muscle originates from the medial epicondyle and supraepicondylar ridge of  the humerus and from a small linear region on the medial edge of the coronoid process of  the ulna (Fig. 7.85A). The median nerve often exits the cubital fossa by passing between the humeral and ulnar heads of  this muscle. The pronator teres crosses the forearm and attaches to an oval rough-ened area on the lateral surface of the radius approximately midway along the bone.
+
+
+
+Table 7.10    Superficial layer of muscles in the anterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
+
+
+Muscle
+Flexor carpi ulnaris
+
+
+Palmaris longus
+
+
+Flexor carpi radialis
+Pronator teres
+
+Origin
+Humeral head—medial epicondyle of humerus; ulnar head—olecranon and posterior border of ulna
+
+Medial epicondyle of humerus
+
+
+
+Medial epicondyle of humerus
+
+Humeral head—medial epicondyle and adjacent supra-epicondylar ridge; ulnar head—medial side of coronoid process
+
+Insertion
+Pisiform bone, and then via pisohamate and pisometacarpal ligaments into the hamate and base of metacarpal V
+Palmar aponeurosis of hand
+
+
+
+Base of metacarpals II and III
+
+Roughening on lateral surface, midshaft, of radius
+
+Innervation
+Ulnar nerve (C7, C8, T1)
+
+
+Median nerve (C7, C8)
+
+
+Median nerve (C6, C7)
+Median nerve (C6, C7)
+
+Function
+Flexes and adducts the wrist joint
+
+
+
+Flexes wrist joint; because the palmar aponeurosis anchors skin of the hand, contraction of the muscle resists shearing forces when gripping
+Flexes and abducts the wrist
+
+Pronation
+
+
+767
+Upper Limb
+
+
+
+
+Ulnar nerve	Ulnar nerve
+
+
+
+
+
+
+Brachial artery
+
+Ulnar artery
+
+
+Radial artery
+
+Humeral head of pronator teres
+
+
+Ulnar head of pronator teres
+
+Median nerve
+
+Flexor carpi radialis
+
+
+
+Humeral head of flexor carpi ulnaris
+
+
+Ulnar head of flexor carpi ulnaris
+
+
+
+Palmaris longus
+Pronator teres (cut)
+
+Flexor carpi ulnaris
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Pisohamate ligament
+
+
+Palmar aponeurosis
+
+
+Pisiform
+
+Pisometacarpal ligament
+
+
+Hook of hamate
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+768	Fig. 7.85  Superficial layer of forearm muscles. A. Superficial muscles (flexor retinaculum not shown). B. Flexor carpi ulnaris muscle.
+Regional Anatomy  •  Anterior Compartment of the Forearm	7
+
+
+
+The  pronator  teres  forms  the  medial  border  of  the cubital fossa and rotates the radius over the ulna during pronation (Table 7.10).
+
+Intermediate layer
+Flexor digitorum superficialis
+The muscle in the intermediate layer of the anterior com-partment of the forearm is the flexor digitorum superfi-cialis muscle (Fig. 7.86). This large muscle has two heads:
+
+In the distal forearm, the flexor digitorum superficialis forms four tendons, which pass through the carpal tunnel of the wrist and into the four fingers. The tendons for the ring and middle fingers are superficial to the tendons for the index and little fingers.
+In the forearm, carpal tunnel, and proximal regions of the four fingers, the tendons of the flexor digitorum super-ficialis are anterior to the tendons of the flexor digitorum profundus muscle.
+
+
+
+
+■     the humero-ulnar head, which originates mainly from the medial epicondyle of  the humerus and from the adjacent medial edge of  the coronoid process of  the ulna; and
+■     the radial head, which originates from the anterior oblique line of the radius.
+
+The median nerve and ulnar artery pass deep to the
+
+Near the base of the proximal phalanx of each finger, the tendon of the flexor digitorum superficialis splits into two parts to pass posteriorly around each side of the tendon of the flexor digitorum profundus and ultimately attach to the margins of the middle phalanx (Fig. 7.86).
+The flexor digitorum superficialis flexes the metacarpo-phalangeal joint and proximal interphalangeal joint of each finger; it also flexes the wrist joint (Table 7.11).
+
+flexor digitorum superficialis between the two heads.
+
+
+
+
+
+
+
+
+Table 7.11    Intermediate layer of muscles in the anterior compartment of the forearm (spinal segment indicated in bold is the major segment innervating the muscle)
+
+
+Muscle
+Flexor digitorum superficialis
+
+Origin
+Humero-ulnar head—medial epicondyle of humerus and adjacent margin of coronoid process; radial head—oblique line of radius
+
+Insertion
+Four tendons, which attach to the palmar surfaces of the middle phalanges of the index, middle, ring, and little fingers
+
+Innervation
+Median nerve (C8, T1)
+
+Function
+Flexes proximal interphalangeal joints of the index, middle, ring, and little fingers; can also flex metacarpophalangeal joints of the same fingers and the wrist joint
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+769
+Upper Limb
+
+
+
+
+
+Ulnar nerve
+
+
+
+
+
+Humero-ulnar head of flexor digitorum superficialis
+
+
+Median nerve Ulnar artery
+
+Interosseous membrane
+
+
+Radial head of flexor digitorum superficialis
+
+
+
+
+Flexor digitorum superficialis
+
+
+
+
+Flexor digitorum profundus
+
+
+
+Flexor pollicis longus
+
+
+
+
+Ulnar nerve
+
+Ulnar artery
+
+Median nerve
+
+
+
+Pronator quadratus
+
+
+Flexor retinaculum	Flexor retinaculum
+
+
+
+
+
+
+
+
+
+
+Flexor digitorum superficialis tendon (cut)
+
+
+
+
+
+
+770	Fig. 7.86  Intermediate layer of forearm muscles.	Fig. 7.87  Deep layer of forearm muscles.
+Regional Anatomy  •  Anterior Compartment of the Forearm	7
+
+
+
+
+Deep layer
+There are three deep muscles in the anterior compartment of the forearm: the flexor digitorum profundus, flexor pol-licis longus, and pronator quadratus (Fig. 7.87).
+
+Flexor digitorum profundus
+The flexor digitorum profundus muscle originates from the anterior and medial surfaces of the ulna and from the adjacent half of the anterior surface of the interosseous membrane (Fig. 7.87). It gives rise to four tendons, which pass through the carpal tunnel into the four medial fingers. Throughout most of their course, the tendons are deep to the tendons of the flexor digitorum superficialis muscle.
+Opposite the proximal phalanx of  each finger, each tendon of the flexor digitorum profundus passes through a split formed in the overlying tendon of the flexor digitorum superficialis muscle and passes distally to insert into the anterior surface of the base of the distal phalanx.
+In the palm, the lumbrical muscles originate from the sides of the tendons of the flexor digitorum profundus (see Fig. 7.108).
+Innervation of  the medial and lateral halves of  the flexor digitorum profundus varies as follows:
+
+The flexor digitorum profundus flexes the metacarpo-phalangeal joints and the proximal and distal interphalan-geal joints of the four fingers. Because the tendons cross the wrist, it can flex the wrist joint as well (Table 7.12).
+
+Flexor pollicis longus
+The flexor pollicis longus muscle originates from the anterior surface of the radius and the adjacent half of the anterior surface of the interosseous membrane (Fig. 7.87). It is a powerful muscle and forms a single large tendon, which passes through the carpal tunnel, lateral to the tendons of  the flexor digitorum superficialis and flexor digitorum profundus muscles, and into the thumb where it attaches to the base of the distal phalanx.
+The flexor pollicis longus flexes the thumb and is inner-vated by the anterior interosseous nerve (branch of  the median nerve) (Table 7.12).
+
+Pronator quadratus
+The pronator quadratus muscle is a flat square-shaped muscle in the distal forearm (Fig. 7.87). It originates from a linear ridge on the anterior surface of the lower end of the ulna and passes laterally to insert onto the flat anterior surface of the radius. It lies deep to, and is crossed by, the tendons of the flexor digitorum profundus and flexor pol-
+
+
+
+■     The lateral half (associated with the index and middle fingers) is innervated by the anterior interosseous nerve (branch of the median nerve).
+■     The medial half (the part associated with the ring and little fingers) is innervated by the ulnar nerve.
+
+licis longus muscles.
+The pronator quadratus muscle pulls the distal end of the radius anteriorly over the ulna during pronation and is innervated by the anterior interosseous nerve (branch of the median nerve) (Table 7.12).
+
+
+
+
+
+
+Table 7.12    Deep layer of muscles in the anterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
+
+
+Muscle
+Flexor digitorum profundus
+
+
+
+Flexor pollicis longus
+
+
+Pronator quadratus
+
+Origin
+Anterior and medial surfaces of ulna and anterior medial half of interosseous membrane
+
+Anterior surface of radius and radial half of interosseous membrane
+
+Linear ridge on distal anterior surface of ulna
+
+Insertion
+Four tendons, which attach to the palmar surfaces of the distal phalanges of the index, middle, ring, and little fingers
+
+Palmar surface of base
+of distal phalanx of thumb
+
+
+Distal anterior surface of radius
+
+Innervation
+Lateral half by median nerve (anterior interosseous nerve); medial half by ulnar nerve (C8, T1)
+
+Median nerve (anterior interosseous nerve) (C7, C8)
+
+
+Median nerve (anterior interosseous nerve) (C7, C8)
+
+Function
+Flexes distal interphalangeal joints of the index, middle, ring, and little fingers; can also flex metacarpophalangeal joints of the same fingers and the wrist joint
+Flexes interphalangeal joint of the thumb; can also flex metacarpophalangeal joint of the thumb
+Pronation
+
+
+
+
+
+
+771
+Upper Limb
+
+
+
+
+Arteries and veins
+The largest arteries in the forearm are in the anterior com-partment, pass distally to supply the hand, and give rise to vessels that supply the posterior compartment (Fig. 7.88). The brachial artery enters the forearm from the arm by passing through the cubital fossa. At the apex of the cubital fossa, it divides into its two major branches, the radial and
+ulnar arteries.
+
+Radial artery
+The radial artery originates from the brachial artery at approximately the neck of the radius and passes along the lateral aspect of the forearm (Fig. 7.88). It is:
+
+■     just deep to the brachioradialis muscle in the proximal half of the forearm,
+■     related on its lateral side to the superficial branch of the
+
+
+
+
+Brachial artery
+
+
+
+
+Supinator
+
+Radial artery
+
+
+Superficial branch of radial nerve
+Posterior interosseous artery
+Pronator teres (cut)
+
+
+
+Ulnar nerve
+
+
+Humeral head of pronator teres
+
+Flexor carpi ulnaris (cut)
+
+Ulnar artery
+
+Common interosseous artery
+Flexor digitorum superficialis (cut)
+Anterior interosseous artery
+
+
+
+radial nerve in the middle third of the forearm, and
+■     medial to the tendon of the brachioradialis muscle and covered only by deep fascia, superficial fascia, and skin in the distal forearm.
+
+
+Perforating branches of anterior
+interosseous artery
+
+
+Flexor digitorum profundus
+
+
+
+In the distal forearm, the radial artery lies immediately lateral to the large tendon of the flexor carpi radialis muscle and directly anterior to the pronator quadratus muscle and the distal end of the radius (Fig. 7.88). In the distal forearm, the radial artery can be located using the flexor carpi radia-lis muscle as a landmark. The radial pulse can be felt by gently palpating the radial artery against the underlying muscle and bone.
+The radial artery leaves the forearm, passes around the lateral side of the wrist, and penetrates the posterolateral aspect of the hand between the bases of metacarpals I and II (Fig. 7.88). Branches of the radial artery in the hand often provide the major blood supply to the thumb and lateral side of the index finger.
+Branches of the radial artery originating in the forearm include:
+
+
+Brachioradialis tendon (cut)
+Flexor pollicis longus
+
+Flexor carpi radialis tendon (cut)
+
+Superficial palmar branch of radial artery
+
+
+Interosseous membrane
+
+Pronator quadratus
+
+Flexor carpi ulnaris tendon (cut)
+Ulnar nerve
+
+
+Deep palmar arch
+
+Superficial palmar arch
+
+■     a radial recurrent artery, which contributes to an	Fig. 7.88  Arteries of the anterior compartment of the forearm. anastomotic network around the elbow joint and to
+
+
+
+
+
+
+
+
+
+
+772
+Regional Anatomy  •  Anterior Compartment of the Forearm	7
+
+
+
+numerous vessels that supply muscles on the lateral side of the forearm (see Fig. 7.66B);
+■     a small palmar carpal branch, which contributes to an  anastomotic  network  of  vessels  that  supply  the carpal bones and joints;
+■     a somewhat larger branch, the superficial palmar branch, which enters the hand by passing through, or
+
+■     the common interosseous artery, which divides into anterior and posterior interosseous arteries (Fig. 7.88); and
+■     two small carpal arteries (dorsal carpal branch and palmar carpal branch), which supply the wrist.
+
+The posterior interosseous artery passes dorsally
+
+
+
+superficial to, the thenar muscles at the base of  the thumb (Fig. 7.88) and anastomoses with the superficial palmar arch formed by the ulnar artery.
+
+Ulnar artery
+The ulnar artery is larger than the radial artery and passes down the medial side of the forearm (Fig. 7.88). It leaves the cubital fossa by passing deep to the pronator teres muscle, and then passes through the forearm in the fascial plane between the flexor carpi ulnaris and flexor digitorum profundus muscles.
+In the distal forearm, the ulnar artery often remains tucked under the anterolateral lip of the flexor carpi ulnaris tendon, and is therefore not easily palpable.
+In distal regions of  the forearm, the ulnar nerve is immediately medial to the ulnar artery.
+The ulnar artery leaves the forearm, enters the hand by passing lateral to the pisiform bone and superficial to the flexor retinaculum of the wrist, and arches over the palm (Fig. 7.88). It is often the major blood supply to the medial three and one-half digits.
+Branches of the ulnar artery that arise in the forearm include:
+
+■     the ulnar recurrent artery with anterior and pos-terior branches, which contribute to an anastomotic network of  vessels around the elbow joint (see Fig. 7.66B);
+■     numerous muscular arteries, which supply surround-ing muscles;
+
+over the proximal margin of the interosseous membrane into the posterior compartment of the forearm.
+The  anterior  interosseous  artery  passes  distally along the anterior aspect of the interosseous membrane and supplies muscles of  the deep compartment of  the forearm  and  the  radius  and  ulna.  It  has  numerous branches, which perforate the interosseous membrane to supply deep muscles of the posterior compartment; it also has a small branch, which contributes to the vascular network around the carpal bones and joints. Perforating the  interosseous  membrane  in  the  distal  forearm,  the anterior  interosseous  artery  terminates  by  joining  the posterior interosseous artery.
+
+Veins
+Deep veins of the anterior compartment generally accom-pany the arteries and ultimately drain into brachial veins associated with the brachial artery in the cubital fossa.
+
+
+In the clinic
+
+Transection of the radial or ulnar artery
+Adult patients may transect the radial or ulnar artery because these vessels are relatively subcutaneous. A typical method of injury is when the hand is forced through a plate glass window. Fortunately, the dual supply to the hand usually enables the surgeon to tie off either the ulnar or the radial artery, without significant consequence.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+773
+Upper Limb
+
+
+
+Nerves
+Nerves in the anterior compartment of the forearm are the median and ulnar nerves and the superficial branch of the radial nerve (Fig. 7.89).
+
+Median nerve
+The median nerve innervates the muscles in the anterior compartment of the forearm except for the flexor carpi ulnaris  and  the  medial  part  of  the  flexor  digitorum profundus (ring and little fingers). It leaves the cubital fossa by passing between the two heads of the pronator teres muscle and passing between the humero-ulnar and radial heads of the flexor digitorum superficialis muscle (Fig. 7.89).
+The median nerve continues a straight linear course distally down the forearm in the fascia on the deep surface of the flexor digitorum superficialis muscle. Just proximal to the wrist, it moves around the lateral side of the muscle and becomes more superficial in position, lying between the tendons of the palmaris longus and flexor carpi radialis muscles. It leaves the forearm and enters the palm of the hand by passing through the carpal tunnel deep to the flexor retinaculum.
+Most branches to the muscles in the superficial and intermediate layers of the forearm originate medially from the nerve just distal to the elbow joint.
+
+■     The largest branch of the median nerve in the forearm is the anterior interosseous nerve, which originates between the two heads of  the pronator teres, passes distally down the forearm with the anterior interosse-ous artery, innervates the muscles in the deep layer (the flexor pollicis longus, the lateral half of the flexor digi-torum  profundus,  and  the  pronator  quadratus)  and terminates as articular branches to joints of the distal forearm and wrist.
+
+
+
+
+Radial nerve
+
+
+
+
+
+Deep branch of radial nerve
+Supinator
+
+Superficial branch
+of radial nerve
+
+Pronator teres (cut)
+
+
+Anterior interosseous nerve
+
+
+
+Brachioradialis tendon (cut)
+
+
+
+
+Flexor carpi radialis tendon (cut)
+
+Palmar branch (of median nerve)
+
+Median nerve
+
+
+Ulnar nerve
+
+
+Humeral head of pronator teres
+
+Flexor carpi ulnaris (cut)
+
+Ulnar head of pronator teres
+
+
+Flexor digitorum superficialis (cut)
+
+
+
+
+
+Flexor digitorum profundus
+
+
+
+
+
+
+Dorsal branch (of ulnar nerve)
+
+
+Flexor carpi ulnaris tendon (cut)
+
+Palmar branch (of ulnar nerve)
+
+■     A small palmar branch originates from the median nerve in the distal forearm immediately proximal to the flexor retinaculum (Fig. 7.89), passes superficially into the hand, and innervates the skin over the base and central palm. This palmar branch is spared in carpal tunnel syndrome because it passes into the hand super-ficial to the flexor retinaculum of the wrist.
+
+
+
+
+
+Fig. 7.89  Nerves of anterior forearm.
+
+
+
+The ulnar nerve enters the anterior compartment of the
+
+
+
+
+Ulnar nerve
+The ulnar nerve passes through the forearm and into the hand, where most of  its major branches occur. In the forearm, the ulnar nerve innervates only the flexor carpi ulnaris muscle and the medial part (ring and little fingers)
+774	of the flexor digitorum profundus muscle (Fig. 7.89).
+
+forearm by passing posteriorly around the medial epicon-dyle of the humerus and between the humeral and ulnar heads of  the flexor carpi ulnaris muscle. After passing down the medial side of the forearm in the plane between the flexor carpi ulnaris and the flexor digitorum profundus muscles, it lies under the lateral lip of the tendon of the flexor carpi ulnaris proximal to the wrist.
+Regional Anatomy  •  Posterior Compartment of the Forearm	7
+
+
+
+The ulnar artery is lateral to the ulnar nerve in the distal two-thirds of the forearm, and both the ulnar artery and nerve enter the hand by passing superficial to the flexor retinaculum and immediately lateral to the pisiform bone (Fig. 7.89).
+
+■     movement of the wrist joint,
+■     extension of the fingers and thumb, and ■     supination.
+
+All muscles in the posterior compartment of the forearm
+
+
+
+In the forearm the ulnar nerve gives rise to:
+
+■     muscular branches to the flexor carpi ulnaris and to the medial half of the flexor digitorum profundus that arise soon after the ulnar nerve enters the forearm; and
+■     two small cutaneous branches—the palmar branch originates in the middle of the forearm and passes into the hand to supply skin on the medial side of the palm; the larger dorsal branch originates from the ulnar nerve in the distal forearm and passes posteriorly deep to the tendon of the flexor carpi ulnaris and innervates skin on the posteromedial side of the back of the hand and most skin on the posterior surfaces of the medial one and one-half digits.
+
+are innervated by the radial nerve.
+
+Superficial layer
+The seven muscles in the superficial layer are the brachio-radialis,  extensor  carpi  radialis  longus,  extensor  carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus (Fig. 7.90). All have a common origin from the supraepicondylar ridge and lateral epicondyle of the humerus and, except for the bra-chioradialis and anconeus, extend as tendons into the hand.
+
+Brachioradialis
+The brachioradialis muscle originates from the proximal
+
+
+
+
+Radial nerve
+The  radial  nerve  bifurcates  into  deep  and  superficial branches under the margin of the brachioradialis muscle in the lateral border of the cubital fossa (Fig. 7.89).
+
+part of  the supraepicondylar ridge of  the humerus and passes through the forearm to insert on the lateral side of the distal end of  the radius just proximal to the radial styloid process (Fig. 7.90).
+In the anatomical position, the brachioradialis is part of
+
+
+
+
+■     The deep branch is predominantly motor and passes between the superficial and deep layers of the supinator muscle to access and supply muscles in the posterior compartment of the forearm.
+■     The superficial branch of the radial nerve is sensory. It passes down the anterolateral aspect of the forearm deep to the brachioradialis muscle and in association with the radial artery. Approximately two-thirds of the way down the forearm, the superficial branch of  the radial  nerve  passes  laterally  and  posteriorly  around the radial side of  the forearm deep to the tendon of the brachioradialis. The nerve continues into the hand where it innervates skin on the posterolateral surface.
+
+the muscle mass overlying the anterolateral surface of the forearm and forms the lateral boundary of  the cubital fossa.
+Because the brachioradialis is anterior to the elbow joint, it acts as an accessory flexor of this joint even though it is in the posterior compartment of the forearm. Its action is most efficient when the forearm is midpronated and it forms a prominent bulge as it acts against resistance.
+The radial nerve emerges from the posterior compart-ment of  the arm just deep to the brachioradialis in the distal arm and innervates the brachioradialis. Lateral to the cubital fossa, the brachioradialis lies over the radial nerve and its bifurcation into deep and superficial branches. In more distal regions, the brachioradialis lies over the
+
+
+POSTERIOR COMPARTMENT OF THE FOREARM
+
+Muscles
+Muscles in the posterior compartment of the forearm occur in two layers: a superficial and a deep layer. The muscles are associated with:
+
+
+
+
+
+775
+Upper Limb
+
+
+
+
+
+
+
+
+Anterior view	Posterior view
+
+
+
+
+
+
+Extensor carpi radialis longus
+Brachioradialis	Anconeus
+
+Extensor carpi radialis brevis
+
+
+
+Extensor carpi ulnaris
+
+
+
+Extensor digiti minimi
+
+
+
+Extensor digitorum
+
+
+
+
+
+Extensor retinaculum
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+Fig. 7.90  Superficial layer of muscles in the posterior compartment of the forearm. A. Brachioradialis muscle (anterior view). B. Superficial 776	muscles (posterior view).
+Regional Anatomy  •  Posterior Compartment of the Forearm	7
+
+
+
+superficial branch of  the radial nerve and radial artery (Table 7.13).
+
+Extensor carpi radialis longus
+The extensor carpi radialis longus muscle originates from the distal part of  the supraepicondylar ridge and the lateral epicondyle of the humerus; its tendon inserts on the dorsal surface of  the base of  metacarpal II (Fig. 7.90). In proximal regions, it is deep to the brachioradialis muscle.
+The extensor carpi radialis longus muscle extends and abducts the wrist, and is innervated by the radial nerve before the nerve divides into superficial and deep branches (Table 7.13).
+
+Extensor carpi radialis brevis
+The extensor carpi radialis brevis muscle originates from the lateral epicondyle of the humerus, and the tendon
+
+inserts onto adjacent dorsal surfaces of the bases of meta-carpals II and III (Fig. 7.90). Along much of its course, the extensor carpi radialis brevis lies deep to the extensor carpi radialis longus.
+The extensor carpi radialis brevis muscle extends and abducts the wrist, and is innervated by the deep branch of the radial nerve before the nerve passes between the two heads of the supinator muscle (Table 7.13).
+
+Extensor digitorum
+The extensor digitorum muscle is the major extensor of the four fingers (index, middle, ring, and little fingers). It originates from the lateral epicondyle of the humerus and forms four tendons, each of which passes into a finger (Fig. 7.90).
+On the dorsal surface of the hand, adjacent tendons of the extensor digitorum are interconnected. In the fingers, each tendon inserts, via a triangular-shaped connective
+
+
+
+
+
+
+
+
+
+Table 7.13    Superficial layer of muscles in the posterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
+
+
+Muscle Brachioradialis
+
+
+
+Extensor carpi radialis longus
+
+
+Extensor carpi radialis brevis
+
+Extensor digitorum
+
+
+
+Extensor digiti minimi
+
+
+
+Extensor carpi ulnaris
+
+Anconeus
+
+Origin
+Proximal part of lateral supraepicondylar ridge of humerus and adjacent intermuscular septum
+Distal part of lateral supraepicondylar ridge of humerus and adjacent intermuscular septum
+Lateral epicondyle of humerus and adjacent intermuscular septum
+Lateral epicondyle of humerus and adjacent intermuscular septum and deep fascia
+
+Lateral epicondyle of humerus and adjacent intermuscular septum together with extensor digitorum
+Lateral epicondyle of humerus and posterior border of ulna
+Lateral epicondyle of humerus
+
+Insertion
+Lateral surface of distal end of radius
+
+
+Dorsal surface of base of metacarpal II
+
+
+Dorsal surface of base of metacarpals II and III
+
+Four tendons, which insert via extensor hoods into the dorsal aspects of the bases of the middle and distal phalanges of the index, middle, ring, and little fingers
+Extensor hood of the little finger
+
+
+
+
+Tubercle on the base of the medial side of metacarpal V
+
+Olecranon and proximal posterior surface of ulna
+
+Innervation
+Radial nerve (C5, C6) before division into superficial and deep branches
+
+Radial nerve (C6, C7) before division into superficial and deep branches
+
+Deep branch of radial nerve (C7, C8) before penetrating supinator muscle
+Posterior interosseous nerve (C7, C8)
+
+
+
+Posterior interosseous nerve (C7, C8)
+
+
+
+Posterior interosseous nerve (C7, C8)
+
+Radial nerve (C6, C7, C8) (via branch to medial head of triceps brachii)
+
+Function
+Accessory flexor of elbow joint when forearm is midpronated
+
+Extends and abducts the wrist
+
+
+Extends and abducts the wrist
+
+Extends the index, middle, ring, and little fingers; can also extend the wrist
+
+
+Extends the little finger
+
+
+
+
+Extends and adducts the wrist
+
+Abduction of the ulna in pronation; accessory
+extensor of the elbow joint	777
+Upper Limb
+
+
+
+tissue aponeurosis (the extensor hood), into the base of the dorsal surfaces of the middle and distal phalanges.
+The extensor digitorum muscle is innervated by the posterior interosseous nerve, which is the continuation of the deep branch of the radial nerve after it emerges from the supinator muscle (Table 7.13).
+
+extensor pollicis brevis, extensor pollicis longus, and exten-sor indicis (Fig. 7.91).
+Except for the supinator muscle, all these deep layer muscles originate from the posterior surfaces of the radius, ulna, and interosseous membrane and pass into the thumb and fingers.
+
+
+
+Extensor digiti minimi
+The extensor digiti minimi muscle is an accessory exten-sor of the little finger and is medial to the extensor digito-rum in the forearm (Fig. 7.90). It originates from the lateral epicondyle of the humerus and inserts, together with the tendon of the extensor digitorum, into the extensor hood of the little finger.
+The extensor digiti minimi is innervated by the posterior interosseous nerve (Table 7.13).
+
+
+■     Three of these muscles—the abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus— emerge from between the extensor digitorum and the extensor carpi radialis brevis tendons of the superficial layer and pass into the thumb.
+■     Two of the three “outcropping” muscles (the abductor pollicis longus and extensor pollicis brevis) form a dis-tinct muscular bulge in the distal posterolateral surface of the forearm.
+
+
+
+Extensor carpi ulnaris
+The extensor carpi ulnarismuscle is medial to the exten-sor digiti minimi (Fig. 7.90). It originates from the lateral epicondyle, and its tendon inserts into the medial side of the base of metacarpal V.
+The extensor carpi ulnaris extends and adducts the wrist, and is innervated by the posterior interosseous nerve
+
+
+All muscles of  the deep layer are innervated by the posterior interosseous nerve, the continuation of the deep branch of the radial nerve.
+
+Supinator
+The  supinator  muscle  has  two  layers,  which  insert together on the proximal aspect of the radius (Fig. 7.91):
+
+
+
+(Table 7.13).
+
+Anconeus
+The anconeus muscle is the most medial of the superficial extensors and has a triangular shape. It originates from the lateral epicondyle of the humerus and has a broad inser-tion into the posterolateral surface of the olecranon and related posterior surface of the ulna (see Fig. 7.84).
+The anconeus abducts the ulna during pronation to
+
+
+■     The more superficial (humeral) layer originates mainly from the lateral epicondyle of  the humerus and the related anular ligament and the radial collateral liga-ment of the elbow joint.
+■     The  deep  (ulnar)  layer  originates  mainly  from  the supinator  crest  on  the  posterolateral  surface  of  the ulna.
+
+maintain the center of the palm over the same point when	From  their  sites  of   origin,  the  two  layers  wrap
+
+the hand is flipped. It is also considered to be an accessory extensor of the elbow joint.
+The anconeus is innervated by the branch of the radial nerve that innervates the medial head of the triceps brachii muscle (Table 7.13).
+
+around  the  posterior  and  lateral  aspect  of  the  head, neck, and proximal shaft of  the radius to insert on the lateral  surface  of  the  radius  superior  to  the  anterior oblique line and to the insertion of  the pronator teres muscle.
+
+
+
+
+Deep layer
+
+The  supinator  muscle  supinates  the  forearm  and hand.
+
+
+
+The deep layer of the posterior compartment of the forearm consists of five muscles: supinator, abductor pollicis longus,
+
+The deep branch of  the radial nerve innervates the supinator muscle and passes to the posterior compartment
+
+
+
+
+
+
+
+
+
+
+778
+Regional Anatomy  •  Posterior Compartment of the Forearm	7
+
+
+
+
+
+Anterior view
+
+
+
+
+
+
+
+Supinator (deep layer)
+
+Supinator (superficial layer)
+
+
+Supinator (superficial layer)
+
+
+Interosseous membrane
+
+
+
+
+
+Abductor pollicis longus
+
+
+Extensor pollicis longus
+
+
+
+Extensor indicis	Extensor pollicis brevis
+
+Extensor carpi radialis longus
+
+Extensor carpi radialis brevis
+Extensor carpi ulnaris
+
+
+
+
+Extensor digitorum
+
+
+
+Extensor pollicis longus
+
+
+Abductor pollicis longus
+Extensor pollicis brevis
+
+
+Muscular bulge on lateral side of distal forearm
+
+
+
+
+
+
+
+
+
+
+Posterior view
+
+
+
+Fig. 7.91  Deep layer of muscles in the posterior compartment of the forearm.	779
+Upper Limb
+
+
+of the forearm by passing between the two heads of this	The  extensor  pollicis  brevis  extends  the  metacarpo-
+
+muscle (Table 7.14).
+
+Abductor pollicis longus
+The abductor pollicis longus muscle originates from the
+
+phalangeal  and  carpometacarpal  joints  of  the  thumb (Table 7.14).
+
+Extensor pollicis longus
+
+
+
+proximal posterior surfaces of the radius and the ulna and from the related interosseous membrane (Fig. 7.91). In the distal forearm, it emerges between the extensor digitorum and extensor carpi radialis brevis muscles to form a tendon that passes into the thumb and inserts on the lateral side of the base of metacarpal I. The tendon contributes to the lateral border of the anatomical snuffbox at the wrist.
+The major function of the abductor pollicis longus is to abduct the thumb at the joint between the metacarpal I and trapezium bones (Table 7.14).
+
+Extensor pollicis brevis
+The extensor pollicis brevis muscle arises distal to the origin of  the abductor pollicis longus from the posterior surface   of   the   radius   and   interosseous   membrane (Fig. 7.91). Together with the abductor pollicis longus, it emerges  between  the  extensor  digitorum  and  extensor carpi radialis brevis muscles to form a bulge on the postero-lateral surface of  the distal forearm. The tendon of  the extensor pollicis brevis passes into the thumb and inserts on the dorsal surface of the base of the proximal phalanx. At the wrist, the tendon contributes to the lateral border of the anatomical snuffbox.
+
+The extensor pollicis longus muscle originates from the posterior surface of  the ulna and adjacent interosseous membrane and inserts via a long tendon into the dorsal surface of  the distal phalanx of  the thumb (Fig. 7.91). Like  the  abductor  pollicis  longus  and  extensor  pollicis brevis, the tendon of  this muscle emerges between the extensor digitorum and the extensor carpi radialis brevis muscles. However, it is held away from the other two deep muscles of  the thumb by passing medially around the dorsal tubercle on the distal end of the radius. The tendon forms the medial margin of  the anatomical snuffbox at the wrist.
+The extensor pollicis longus extends all joints of  the thumb (Table 7.14).
+
+Extensor indicis
+The extensor indicis muscle is an accessory extensor of the index finger. It originates distal to the extensor pollicis longus from the posterior surface of the ulna and adjacent interosseous membrane (Fig. 7.91). The tendon passes into the hand and inserts into the extensor hood of the index finger with the tendon of  the extensor digitorum (Table 7.14).
+
+
+
+
+Table 7.14    Deep layer of muscles in the posterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
+
+
+Muscle Supinator
+
+
+
+Abductor pollicis longus
+
+
+Extensor pollicis brevis
+
+
+
+Extensor pollicis longus
+
+
+
+Extensor indicis
+
+780
+
+Origin
+Superficial layer—lateral epicondyle of humerus, radial collateral and anular ligaments; deep layer—supinator crest of the ulna
+Posterior surfaces of ulna and radius (distal to the attachments of supinator and anconeus), and intervening interosseous membrane
+Posterior surface of radius (distal to abductor pollicis longus) and the adjacent interosseous membrane
+
+
+Posterior surface of ulna (distal to the abductor pollicis longus) and the adjacent interosseous membrane
+
+
+Posterior surface of ulna (distal to extensor pollicis longus) and adjacent interosseous membrane
+
+Insertion
+Lateral surface of radius superior to the anterior oblique line
+
+Lateral side of base of metacarpal I
+
+
+Dorsal surface of base of proximal phalanx of the thumb
+
+
+Dorsal surface of base of distal phalanx of thumb
+
+
+Extensor hood of index finger
+
+Innervation
+Posterior interosseous nerve (C6, C7)
+
+
+Posterior interosseous nerve (C7, C8)
+
+
+Posterior interosseous nerve (C7, C8)
+
+
+
+Posterior interosseous nerve (C7, C8)
+
+
+
+Posterior interosseous nerve (C7, C8)
+
+Function Supination
+
+
+
+Abducts carpometacarpal joint of thumb; accessory extensor of the thumb
+
+Extends metacarpophalangeal joint of the thumb; can also extend the carpometacarpal joint of the thumb
+Extends interphalangeal joint of the thumb; can also extend carpometacarpal and metacarpophalangeal joints of the thumb
+Extends index finger
+Regional Anatomy  •  Posterior Compartment of the Forearm	7
+
+
+
+
+Arteries and veins
+The blood supply to the posterior compartment of  the forearm occurs predominantly through branches of  the radial, posterior interosseous, and anterior interosseous arteries (Fig. 7.92).
+
+Posterior interosseous artery
+The posterior interosseous artery originates in the anterior compartment from the common interosseous branch of
+
+the ulnar artery and passes posteriorly over the proximal margin of the interosseous membrane and into the poste-rior compartment of the forearm. It contributes a branch, the recurrent interosseous artery (see Fig. 7.66B), to the vascular network around the elbow joint and then passes between the supinator and abductor pollicis longus muscles to supply the superficial extensors. After receiving the terminal end of the anterior interosseous artery, the posterior interosseous artery terminates by joining the dorsal carpal arch of the wrist.
+
+
+
+Radial nerve
+
+Branch to brachioradialis
+
+Branch to extensor carpi radialis longus
+
+Branch to extensor carpi radialis brevis
+
+
+Deep branch
+
+
+Superficial branch
+
+
+Posterior interosseous artery
+
+
+Interosseous membrane
+
+
+
+Common interosseous artery
+
+Anterior interosseous artery
+
+Ulnar artery
+
+
+Posterior interosseous nerve (continuation of deep branch of radial nerve)
+
+
+
+Posterior interosseous artery
+
+
+Anterior view
+
+
+
+
+
+
+
+Posterior view
+
+
+Anterior interosseous artery
+
+
+
+
+
+
+
+
+
+Fig. 7.92  Posterior interosseous artery and radial nerve in posterior compartment of forearm.	781
+Upper Limb
+
+
+
+
+Anterior interosseous artery
+The anterior interosseous artery, also a branch of  the common interosseous branch of the ulnar artery, is situ-
+
+HAND
+
+The hand (Fig. 7.93) is the region of the upper limb distal to the wrist joint. It is subdivided into three parts:
+
+ated in the anterior compartment of the forearm on the interosseous  membrane.  It  has  numerous  perforating branches, which pass directly through the interosseous membrane to supply deep muscles of the posterior com-partment. The terminal end of the anterior interosseous artery  passes  posteriorly  through  an  aperture  in  the
+
+
+■     the wrist (carpus),
+■     the metacarpus, and
+■     the digits (five fingers including the thumb).
+
+The five digits consist of the laterally positioned thumb
+
+
+
+interosseous membrane in distal regions of the forearm to join the posterior interosseous artery.
+
+Radial artery
+The radial artery has muscular branches, which contribute to the supply of the extensor muscles on the radial side of the forearm.
+
+Veins
+
+and, medial to the thumb, the four fingers—the index, middle, ring, and little fingers.
+In the normal resting position, the fingers form a flexed arcade, with the little finger flexed most and the index finger flexed least. In the anatomical position, the fingers are extended.
+The hand has an anterior surface (palm) and a dorsal surface (dorsum of hand).
+Abduction and adduction of the fingers are defined with
+
+Deep   veins   of   the   posterior   compartment   generally	respect to the long axis of the middle finger (Fig. 7.93). In accompany the arteries. They ultimately drain into bra-	the anatomical position, the long axis of  the thumb is chial  veins  associated  with  the  brachial  artery  in  the
+cubital fossa.	Adduction	Adduction
+
+
+
+Nerves Radial nerve
+The nerve of the posterior compartment of the forearm is the radial nerve (Fig. 7.92). Most of the muscles are inner-vated by the deep branch, which originates from the radial nerve in the lateral wall of the cubital fossa deep to the brachioradialis muscle and becomes the posterior inter-osseous nerve after emerging from between the superficial and deep layers of the supinator muscle in the posterior compartment of the forearm.
+In the lateral wall of the cubital fossa, and before divid-ing into superficial and deep branches, the radial nerve innervates the brachioradialis and extensor carpi radialis longus muscles.
+The deep branch innervates the extensor carpi radialis brevis, then passes between the two layers of the supinator muscle and follows the plane of  separation between the two layers dorsally and laterally around the proximal shaft of the radius to the posterior aspect of the forearm. It sup-
+
+
+Fingers
+
+Abduction	Middle
+
+Ring
+
+Little
+
+
+Digits of the hand
+
+
+
+Metacarpals
+
+
+
+Carpal bones
+
+Wrist joint
+
+
+Index
+
+Abduction
+
+
+
+
+
+
+Thumb
+
+
+
+
+
+
+
+
+
+
+Distal skin crease
+
+plies the supinator muscle and then emerges, as the poste-rior interosseous nerve, from the muscle to lie between the superficial and deep layers of muscles.
+The posterior interosseous nerve supplies the remaining
+
+
+Proximal skin crease
+
+Ulna	Radius
+
+
+
+muscles in the posterior compartment and terminates as articular branches, which pass deep to the extensor pollicis longus muscle to reach the wrist.
+782
+
+
+Fig. 7.93  Right hand. The fingers are shown in a normal resting arcade in which they are flexed. In the anatomical position, the digits are straight and adducted.
+Regional Anatomy  •  Hand	7
+
+
+
+rotated 90° to the rest of the digits so that the pad of the thumb points medially; consequently, movements of  the thumb are defined at right angles to the movements of the other digits of the hand.
+
+■     the capitate, which has a head, and
+■     the hamate, which has a hook (Fig. 7.94).
+
+The trapezium articulates with the metacarpal bone of
+
+
+
+The hand is a mechanical and sensory tool. Many of the features of the upper limb are designed to facilitate posi-tioning the hand in space.
+
+
+Bones
+There are three groups of bones in the hand:
+
+the thumb and has a distinct tubercle on its palmar surface that projects anteriorly.
+The largest of the carpal bones, the capitate, articulates with the base of metacarpal III.
+The hamate, which is positioned just lateral and distal to the pisiform, has a prominent hook (hook of hamate) on its palmar surface that projects anteriorly.
+
+
+
+■     The eight carpal bones are the bones of the wrist.
+■     The five metacarpals (I to V) are the bones of  the metacarpus.
+■     The phalanges are the bones of the digits—the thumb has only two; the rest of the digits have three (Fig. 7.94).
+
+The carpal bones and metacarpals of the index, middle,
+
+Articular surfaces
+The  carpal  bones  have  numerous  articular  surfaces (Fig. 7.94). All of them articulate with each other, and the carpal bones in the distal row articulate with the metacar-pals of the digits. With the exception of the metacarpal of the thumb, all movements of the metacarpal bones on the carpal bones are limited.
+
+ring, and little fingers (metacarpals II to V) tend to function	The  expansive  proximal  surfaces  of   the  scaphoid
+
+as a unit and form much of the bony framework of the palm. The metacarpal of  the thumb functions indepen-dently and has increased flexibility at the carpometacarpal joint to provide opposition of the thumb to the fingers.
+
+Carpal bones
+The small carpal bones of the wrist are arranged in two rows, a proximal and a distal row, each consisting of four bones (Fig. 7.94).
+
+Proximal row
+From lateral to medial and when viewed from anteriorly, the proximal row of bones consists of:
+
+and lunate articulate with the radius to form the wrist joint.
+
+Carpal arch
+The carpal bones do not lie in a flat plane; rather, they form an arch, whose base is directed anteriorly (Fig. 7.94). The lateral side of  this base is formed by the tubercles of the scaphoid and trapezium. The medial side is formed by the pisiform and the hook of the hamate.
+The flexor retinaculum attaches to, and spans the dis-tance between, the medial and lateral sides of the base to form the anterior wall of the so-called carpal tunnel. The sides and roof of the carpal tunnel are formed by the arch
+
+
+
+
+■     the boat-shaped scaphoid,
+■     the lunate, which has a crescent shape, ■     the three-sided triquetrum bone, and
+■     the pea-shaped pisiform (Fig. 7.94).
+
+of the carpal bones.
+
+Metacarpals
+Each of the five metacarpals is related to one digit:
+
+
+
+
+The pisiform is a sesamoid bone in the tendon of the flexor  carpi  ulnaris  and  articulates  with  the  anterior surface of the triquetrum.
+The scaphoid has a prominent tubercle on its lateral
+
+■     Metacarpal I is related to the thumb.
+■     Metacarpals II to V are related to the index, middle, ring, and little fingers, respectively (Fig. 7.94).
+
+Each metacarpal consists of a base, a shaft (body), and
+
+
+
+palmar surface that is directed anteriorly.
+
+Distal row
+From lateral to medial and when viewed from anteriorly, the distal row of carpal bones consists of:
+
+distally, a head.
+All of the bases of the metacarpals articulate with the carpal bones; in addition, the bases of  the metacarpal bones of the fingers articulate with each other.
+All of  the heads of  the metacarpals articulate with the proximal phalanges of the digits. The heads form the
+
+
+
+■     the irregular four-sided trapezium bone, ■     the four-sided trapezoid,
+
+knuckles on the dorsal surface of  the hand when the fingers are flexed.
+783
+Upper Limb
+
+
+
+
+
+
+Distal
+
+
+
+Middle
+
+
+
+
+
+Proximal
+
+
+Phalanges
+
+Distal
+
+
+
+
+
+III IV
+Metacarpals	V
+
+Proximal
+II
+
+
+
+Capitate
+
+Hook of hamate
+
+
+I
+
+Trapezoid
+
+
+
+Carpal bones                 Hamate Pisiform
+
+Triquetrum
+
+Lunate
+
+
+Ulna
+
+Tubercle of trapezium
+
+Trapezium	Carpal bones
+
+Tubercle of scaphoid
+
+Scaphoid
+
+Wrist joint
+
+Radius
+
+
+
+
+
+
+Pisiform
+
+Triquetrum
+
+Hamate
+
+A	Carpal arch
+
+Tubercle
+
+Trapezium
+
+Trapezoid
+Capitate	Carpal arch
+
+
+Fig. 7.94  Right hand and wrist joint. A. Bones.
+
+
+
+
+
+784
+Regional Anatomy  •  Hand	7
+
+
+Triquetrum	Lunate	Scaphoid
+
+
+
+
+
+
+Phalanges
+
+
+
+
+
+
+
+
+Metacarpals
+
+
+
+Carpal bones
+
+B	C
+
+Ulna	Radius	Ulna	Articular disc	Radius
+
+Fig. 7.94, cont’d  Right hand and wrist joint. B. Radiograph of a normal hand and wrist joint (anteroposterior view). C. Magnetic resonance image of a normal wrist joint in the coronal plane.
+
+
+
+Phalanges
+The phalanges are the bones of the digits (Fig. 7.94):
+
+with the corresponding concave surface of the radius and articular disc.
+The wrist joint allows movement around two axes. The
+
+
+
+
+■     The  thumb  has  two—a  proximal  and  a  distal phalanx.
+■     The rest of the digits have three—a proximal, a middle, and a distal phalanx.
+
+Each phalanx has a base, a shaft (body), and distally,
+
+hand can be abducted, adducted, flexed, and extended at the wrist joint.
+Because the radial styloid process extends further dis-tally than does the ulnar styloid process, the hand can be adducted to a greater degree than it can be abducted.
+The capsule of the wrist joint is reinforced by palmar radiocarpal, palmar ulnocarpal, and dorsal radio-
+
+
+
+a head.
+The base of each proximal phalanx articulates with the head of the related metacarpal bone.
+The head of  each distal phalanx is nonarticular and flattened into a crescent-shaped palmar tuberosity, which lies under the palmar pad at the end of the digit.
+
+
+Joints Wrist joint
+The wrist joint is a synovial joint between the distal end of the radius and the articular disc overlying the distal end of the ulna, and the scaphoid, lunate, and triquetrum (Fig. 7.94). Together, the articular surfaces of the carpals form an oval shape with a convex contour, which articulates
+
+carpal ligaments. In addition, radial and ulnar col-lateral ligaments of the wrist joint span the distance between the styloid processes of the radius and ulna and the adjacent carpal bones. These ligaments reinforce the medial and lateral sides of the wrist joint and support them during flexion and extension.
+
+Carpal joints
+The  synovial  joints  between  the  carpal  bones  share  a common articular cavity. The joint capsule of the joints is reinforced by numerous ligaments.
+Although movement at the carpal joints (intercarpal joints) is limited, the joints do contribute to the positioning of the hand in abduction, adduction, flexion, and, particu-
+larly, extension.	785
+Upper Limb
+
+
+
+Carpometacarpal joints
+There are five carpometacarpal joints between the meta-
+
+Deep transverse metacarpal ligaments
+
+carpals  and  the  related  distal  row  of   carpal  bones (Fig. 7.94).
+
+The saddle joint, between metacarpal I and the trape-zium, imparts a wide range of mobility to the thumb that is not a feature of the rest of the digits. Movements at this carpometacarpal joint are flexion, extension, abduction, adduction, rotation, and circumduction.
+The carpometacarpal joints between metacarpals II to V and the carpal bones are much less mobile than the carpometacarpal joint of the thumb, allowing only limited
+
+
+
+
+
+
+Capsule of metacarpo-phalangeal joint
+
+gliding  movements.  Movement  of  the  joints  increases
+
+medially, so metacarpal V slides to the greatest degree. This can be best observed on the dorsal surface of the hand as it makes a fist.
+
+Metacarpophalangeal joints
+The joints between the distal heads of the metacarpals and the proximal phalanges of the digits are condylar joints, which allow flexion, extension, abduction, adduction, cir-cumduction, and limited rotation (Fig. 7.94). The capsule of each joint is reinforced by the palmar ligament and by medial and lateral collateral ligaments.
+
+
+
+
+
+
+
+
+Palmar ligament
+
+
+Deep transverse metacarpal ligaments
+The  three  deep  transverse  metacarpal  ligaments
+
+(Fig. 7.95) are thick bands of connective tissue connecting the palmar ligaments of the metacarpophalangeal joints of the fingers to each other. They are important because, by linking the heads of the metacarpal bones together, they restrict the movement of these bones relative to each other. As a result, they help form a unified skeletal framework for the palm of the hand.
+Significantly,  a  deep  transverse  metacarpal  ligament does not occur between the palmar ligament of the meta-carpophalangeal joint of the thumb and the palmar liga-
+
+
+
+
+
+Fig. 7.95  Deep transverse metacarpal ligaments, right hand.
+
+
+
+
+
+Interphalangeal joints of hand
+
+ment of the index finger. The absence of this ligament, and	The  interphalangeal  joints  of  the  hand  are  hinge
+
+the presence of a saddle joint between metacarpal I and the trapezium, are responsible for the increased mobility of the thumb relative to the rest of the digits of the hand.
+
+joints that allow mainly flexion and extension. They are reinforced by medial and lateral collateral ligaments and palmar ligaments.
+
+
+
+
+
+
+
+
+
+
+
+786
+Regional Anatomy  •  Hand	7
+
+
+
+In the clinic
+
+Fracture of the scaphoid and avascular necrosis of the proximal scaphoid
+The commonest carpal injury is a fracture across the waist of the scaphoid bone (Fig. 7.96). It is uncommon to see other injuries. In approximately 10% of individuals, the scaphoid bone has a sole blood supply from the radial artery, which
+
+
+
+enters through the distal portion of the bone to supply the proximal portion. When a fracture occurs across the waist of the scaphoid, the proximal portion therefore undergoes avascular necrosis. It is impossible to predict which patients have this blood supply.
+
+
+
+Hamate
+Pisiform
+
+Capitate	Trapezium
+Trapezoid
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B
+
+
+Ulna
+Triquetrum
+
+Scaphoid	Fracture
+Lunate	Radius
+
+
+Fig. 7.96  Wrist radiographs (posteroanterior view). A. Normal. B. Scaphoid fracture.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+787
+Upper Limb
+
+
+
+In the clinic
+
+Kienbock’s disease
+Interruption of the blood supply to the lunate can lead to avascular necrosis of the lunate, known as Kienbock’s disease (Fig. 7.97). This can cause pain and stiffness and arthritis in the longer term.
+
+
+Lunate
+
+
+Carpal tunnel and structures at the wrist
+The carpal tunnel is formed anteriorly at the wrist by a deep arch formed by the carpal bones and the flexor reti-naculum (see Fig. 7.94).
+The base of the carpal arch is formed medially by the pisiform and the hook of the hamate and laterally by the tubercles of the scaphoid and trapezium.
+The flexor retinaculum is a thick connective tissue liga-ment that bridges the space between the medial and lateral sides of the base of the arch and converts the carpal arch into the carpal tunnel.
+The four tendons of the flexor digitorum profundus, the four tendons of the flexor digitorum superficialis, and the tendon of the flexor pollicis longus pass through the carpal tunnel, as does the median nerve (Fig. 7.98).
+The flexor retinaculum holds the tendons to the bony plane at the wrist and prevents them from “bowing.”
+Free movement of the tendons in the carpal tunnel is
+
+facilitated  by  synovial  sheaths,  which  surround  the
+
+
+
+
+
+
+
+
+
+
+
+
+
+Fig. 7.97  Radiograph of wrist showing sclerosis in the lunate consistent with avascular necrosis (Kienbock’s disease).
+
+tendons. All the tendons of the flexor digitorum profundus and flexor digitorum superficialis are surrounded by a single synovial sheath; a separate sheath surrounds the tendon of the flexor pollicis longus. The median nerve is anterior to the tendons in the carpal tunnel.
+The tendon of the flexor carpi radialis is surrounded by a synovial sheath and passes through a tubular compart-ment formed by the attachment of the lateral aspect of the flexor retinaculum to the margins of a groove on the medial side of the tubercle of the trapezium.
+The ulnar artery, ulnar nerve, and tendon of the pal-maris longus pass into the hand anterior to the flexor reti-naculum and therefore do not pass through the carpal tunnel (Fig. 7.98). The tendon of the palmaris longus is not surrounded by a synovial sheath.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+788
+Regional Anatomy  •  Hand	7
+
+
+
+The radial artery passes dorsally around the lateral side of the wrist and lies adjacent to the external surface of the scaphoid.
+The extensor tendons pass into the hand on the medial, lateral, and posterior surfaces of the wrist in six compart-ments defined by an extensor retinaculum and lined by synovial sheaths (Fig. 7.98):
+
+■     The tendons of  the extensor digitorum and extensor indicis share a compartment and synovial sheath on the posterior surface of the wrist.
+■     The tendons of the extensor carpi ulnaris and extensor digiti minimi have separate compartments and sheaths on the medial side of the wrist.
+■     The tendons of the abductor pollicis longus and exten-sor pollicis brevis muscles, the extensor carpi radialis longus and extensor carpi radialis brevis muscles, and the extensor pollicis longus muscle pass through three compartments on the lateral surface of the wrist.
+
+
+
+In the clinic
+
+Median artery
+A large median artery is an anatomical variant found in some individuals, where a persistent artery runs alongside the median nerve in one or both forearms and through the carpal tunnel. Individuals are at risk from heavy bleeding from deep cuts to the wrist.
+
+
+In the clinic
+
+Carpal tunnel syndrome
+Carpal tunnel syndrome is an entrapment syndrome caused by pressure on the median nerve within the carpal tunnel. The etiology of this condition is often obscure, though in some instances the nerve injury may be a direct effect of increased pressure on the median nerve caused by overuse, swelling of the tendons and tendon sheaths (e.g., rheumatoid arthritis), and cysts arising from the carpal joints. Increased pressure in the carpal tunnel is thought to cause venous congestion that produces nerve edema and anoxic damage to the capillary endothelium of the median nerve itself.
+Patients typically report pain and pins-and-needles sensations in the distribution of the median nerve. Weakness and loss of muscle bulk of the thenar muscles may also occur. Gently tapping over the median nerve (in the region of the flexor retinaculum) readily produces these symptoms (Tinel’s sign).
+Initial treatment is aimed at reducing the inflammation and removing any repetitive insults that produce the symptoms. If this does not lead to improvement, nerve conduction studies will be necessary to confirm nerve entrapment, which may require surgical decompression of the flexor retinaculum.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+789
+Upper Limb
+
+
+
+Palmaris longus tendon
+
+Ulnar artery
+
+Ulnar nerve
+
+Flexor digitorum superficialis tendons
+
+Carpal tunnel
+
+Flexor digitorum profundus tendons
+
+
+Extensor carpi ulnaris tendon
+
+Basilic vein
+
+Extensor digiti minimi tendon
+
+
+Flexor retinaculum
+
+Median nerve
+
+Flexor carpi radialis tendon
+
+Flexor pollicis longus tendon
+
+
+Abductor pollicis longus tendon
+
+
+Extensor pollicis brevis tendon
+
+Cephalic vein
+
+Radial artery
+
+Extensor pollicis longus tendon
+
+Extensor carpi radialis longus tendon
+
+
+
+
+A
+
+Ulnar nerve
+
+
+
+
+Ulnar artery Median nerve
+
+
+Extensor digitorum tendons
+
+
+
+Flexor retinaculum
+
+Extensor carpi radialis brevis tendon
+
+Extensor indicis tendon
+
+
+
+Flexor digitorum superficialis and profundus tendons
+
+
+Radial artery
+Radial nerve    Carpal arch
+Flexor tendons
+Extensor tendons
+Median nerve	Carpal tunnel
+
+Flexor digitorum superficialis tendons
+
+Flexor digitorum profundus tendons
+
+Flexor pollicis longus tendon
+
+Flexor carpi radialis tendon
+
+
+
+
+
+
+
+
+
+
+
+
+
+B
+
+Hamate    Capitate	Trapezoid	Trapezium	C
+
+Fig. 7.98  Carpal tunnel. A. Structure and relations. B. Magnetic resonance image of a normal wrist in the axial plane. C. Magnetic resonance image of a normal wrist in the coronal plane.
+
+
+
+790
+Regional Anatomy  •  Hand	7
+
+
+Palmar aponeurosis
+The palmar aponeurosis is a triangular condensation of deep fascia that covers the palm and is anchored to the skin in distal regions (Fig. 7.99).
+The apex of the triangle is continuous with the palmaris longus tendon, when present; otherwise, it is anchored to the flexor retinaculum. From this point, fibers radiate to extensions at the bases of the digits that project into each of the index, middle, ring, and little fingers and, to a lesser extent, the thumb.
+Transverse fibers interconnect the more longitudinally arranged bundles that continue into the digits.
+Vessels, nerves, and long flexor tendons lie deep to the palmar aponeurosis in the palm.
+
+In the clinic
+
+Dupuytren’s contracture
+The palmar fascia can become abnormally thickened in certain individuals, causing the fingers to progressively develop a fixed flexion position. This results in loss of dexterity and function, and in severe cases requires surgical removal of the abnormal tissue.
+
+Palmaris brevis
+The palmaris brevis, a small intrinsic muscle of the hand, is a quadrangular-shaped subcutaneous muscle that over-lies the hypothenar muscles, ulnar artery, and superficial branch of the ulnar nerve at the medial side of the palm (Fig. 7.99). It originates from the palmar aponeurosis and flexor retinaculum and inserts into the dermis of the skin on the medial margin of the hand.
+The palmaris brevis deepens the cup of  the palm by pulling on skin over the hypothenar eminence and forming a distinct ridge. This may improve grip.
+The palmaris brevis is innervated by the superficial branch of the ulnar nerve.
+
+Anatomical snuffbox
+The “anatomical snuffbox” is a term given to the triangular depression formed on the posterolateral side of the wrist and metacarpal I by the extensor tendons passing into the thumb (Fig. 7.100). Historically, ground tobacco (snuff) was placed in this depression before being inhaled into the nose. The base of the triangle is at the wrist and the apex is directed into the thumb. The impression is most apparent when the thumb is extended:
+
+
+
+Longitudinal fibers of palmar aponeurosis
+
+Transverse fibers
+of palmar aponeurosis
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+First dorsal interosseous muscle
+
+Radial artery
+
+
+
+
+
+Palmaris brevis muscle
+
+
+
+
+
+Fig. 7.99  Palmar aponeurosis, right hand.
+
+
+
+Anatomical snuffbox
+
+Extensor pollicis longus tendon
+Cephalic vein
+
+Fig. 7.100  Anatomical snuffbox, left hand.
+
+Radial artery
+
+
+Extensor pollicis brevis tendon
+
+Abductor pollicis longus tendon
+791
+Upper Limb
+
+
+
+■     The  lateral  border  is  formed  by  the  tendons  of  the abductor pollicis longus and extensor pollicis brevis.
+■     The medial border is formed by the tendon of the exten-sor pollicis longus.
+■     The floor of the impression is formed by the scaphoid and trapezium, and the distal ends of the tendons of the extensor carpi radialis longus and extensor carpi radialis brevis.
+
+The radial artery passes obliquely through the anatomi-
+
+
+In the clinic
+
+Snuffbox
+The anatomical snuffbox is an important clinical region. When the hand is in ulnar deviation, the scaphoid becomes palpable within the snuffbox. This position enables the physician to palpate the bone to assess for a fracture. The pulse of the radial artery can also be felt in the snuffbox.
+
+
+
+cal snuffbox, deep to the extensor tendons of the thumb and lies adjacent to the scaphoid and trapezium.
+Terminal parts of the superficial branch of the radial nerve pass subcutaneously over the snuffbox as does the origin of the cephalic vein from the dorsal venous arch of the hand.
+
+Deep transverse metacarpal ligament
+
+
+Fibrous digital sheaths
+After exiting the carpal tunnel, the tendons of the flexor digitorum superficialis and profundus muscles cross the palm and enter fibrous sheaths on the palmar aspect of the digits (Fig. 7.101). These fibrous sheaths:
+
+Synovial sheath
+
+
+
+
+Flexor digitorum profundus tendon
+
+
+Fibrous digital sheaths
+
+
+
+
+
+
+Flexor digitorum superficialis tendon
+
+
+Palmar ligament
+
+
+
+
+
+
+Synovial sheath of flexor pollicis longus tendon
+
+
+Synovial sheath	Flexor retinaculum
+
+
+
+
+
+
+
+792	Fig. 7.101  Fibrous digital sheaths and synovial sheaths of the right hand.
+Regional Anatomy  •  Hand	7
+
+
+
+■     begin proximally, anterior to the metacarpophalangeal joints, and extend to the distal phalanges;
+■     are formed by fibrous arches and cruciate (cross-shaped) ligaments, which are attached posteriorly to the margins of the phalanges and to the palmar ligaments associated with  the  metacarpophalangeal  and  interphalangeal joints; and
+■     hold the tendons to the bony plane and prevent the tendons from bowing when the digits are flexed.
+
+Within each tunnel, the tendons are surrounded by a synovial sheath. The synovial sheaths of the thumb and little finger are continuous with the sheaths associated with the tendons in the carpal tunnel (Fig. 7.101).
+
+Extensor hoods
+The tendons of the extensor digitorum and extensor pol-licis longus muscles pass onto the dorsal aspect of the digits
+
+In the clinic
+
+De Quervain’s syndrome
+De Quervain’s syndrome is an inflammatory disorder that occurs within the first dorsal extensor compartment and involves the extensor pollicis brevis tendon and abductor pollicis longus tendon and their common tendon sheath (Fig. 7.102). Patients typically present with significant wrist pain preventing appropriate flexion/extension and abduction of the thumb. The cause of this disorder is often overuse. For example, the syndrome is common in young mothers who are constantly lifting young children. Other causes include inflammatory disorders such as rheumatoid arthritis.
+
+
+In the clinic
+
+Tenosynovitis
+Tenosynovitis is inflammation of a tendon and its sheath. The condition may be caused by overuse; however, it can also be associated with other disorders such as rheumatoid arthritis and connective tissue pathologies. If the inflammation becomes severe and ensuing fibrosis occurs, the tendon will not run smoothly within the tendon sheath, and typically within the fingers the tendon may stick or require excess force to fully extend and flex, producing a “triggering” phenomenon.
+
+
+In the clinic
+
+Trigger finger
+Trigger finger is a common disorder of late childhood and adulthood and is typically characterized by catching or snapping and occasionally locking of the flexor tendon(s) in the hand. Trigger finger can be associated with significant dysfunction and pain. The triggering is usually related to fibrosis and tightening of the flexor tendon sheath at the level of the metacarpophalangeal joint.
+
+
+and expand over the proximal phalanges to form complex “extensor hoods” or “dorsal digital expansions” (Fig. 7.103A). The tendons of the extensor digiti minimi, exten-sor indicis, and extensor pollicis brevis muscles join these hoods.
+Each extensor hood is triangular, with:
+
+■     the apex attached to the distal phalanx,
+
+
+
+
+1st extensor compartment
+
+■     the  central  region  attached  to  the  middle  phalanx (index,  middle,  ring,  and  little  fingers)  or  proximal phalanx (thumb), and
+■     each corner of the base wrapped around the sides of the metacarpophalangeal joint—in the index, middle, ring, and little fingers, the corners of the hoods attach mainly to the deep transverse metacarpal ligaments; in the thumb, the hood is attached on each side to muscles.
+
+
+
+
+
+
+
+
+
+
+
+Fig. 7.102  MRI of the wrist showing fluid and inflammation associated with the first extensor compartment, consistent with De Quervain’s tenosynovitis.
+
+In addition to other attachments, many of the intrinsic muscles of the hand insert into the free margin of the hood on each side. By inserting into the extensor hood, these intrinsic  muscles  are  responsible  for  complex  delicate movements of the digits that could not be accomplished with the long flexor and extensor tendons alone.
+In the index, middle, ring, and little fingers, the lumbri-cal, interossei, and abductor digiti minimi muscles attach to the extensor hoods. In the thumb, the adductor pollicis and abductor pollicis brevis muscles insert into and anchor
+the extensor hood.	793
+Upper Limb
+
+
+
+Extensor digitorum tendon
+
+Dorsal interosseous
+muscle	Extensor hood
+Middle finger
+
+
+
+
+
+
+
+
+
+Flexor digitorum profundus tendon
+A	Lumbrical muscle
+
+Deep transverse metacarpal ligament
+
+Palmar ligament
+
+
+
+Fulcrum of metacarpophalangeal joint
+
+Fulcrums of interphalangeal joints
+
+
+
+
+
+
+
+
+Flexion of metacarpophalangeal joint
+
+
+
+
+
+
+
+Contraction of intrinsic muscles (lumbricals and interossei muscles)
+
+Extension of interphalangeal joints
+
+
+
+
+B
+Flexed	Extended
+
+
+Upstroke
+
+
+
+
+
+C
+
+Fig. 7.103  Extensor hood. A and B. Middle finger, left hand. C. Function of extensor hoods and intrinsic muscles.
+
+
+
+
+
+
+794
+Regional Anatomy  •  Hand	7
+
+
+
+Because force from the small intrinsic muscles of  the hand is applied to the extensor hood distal to the fulcrum of the metacarpophalangeal joints, the muscles flex these joints (Fig. 7.103B). Simultaneously, the force is trans-ferred dorsally through the hood to extend the interpha-langeal joints. This ability to flex the metacarpophalangeal joints, while at the same time extending the interphalan-geal joints, is entirely due to the intrinsic muscles of the hand working through the extensor hoods. This type of precision movement is used in the upstroke when writing a t (Fig. 7.103C).
+
+
+Muscles
+The intrinsic muscles of the hand are the palmaris brevis (described on p. 791; see Fig. 7.99), interossei, adductor pollicis, thenar, hypothenar, and lumbrical muscles (Figs. 7.104 to 7.108). Unlike the extrinsic muscles that originate in  the  forearm,  insert  in  the  hand,  and  function  in
+
+forcefully  gripping  (“power  grip”)  with  the  hand,  the intrinsic muscles occur entirely in the hand and mainly execute precision movements (“precision grip”) with the fingers and thumb.
+All of the intrinsic muscles of the hand are innervated by the deep branch of the ulnar nerve except for the three thenar and two lateral lumbrical muscles, which are inner-vated by the median nerve. The intrinsic muscles are pre-dominantly innervated by spinal cord segment T1 with a contribution from C8.
+The interossei are muscles between and attached to the metacarpals (Figs. 7.104 and 7.105). They insert into the proximal phalanx of each digit and into the extensor hood and are divided into two groups, the dorsal interossei and the palmar interossei. All of the interossei are innervated by the deep branch of  the ulnar nerve. Collectively, the interossei abduct and adduct the digits and contribute to the complex flexion and extension movements generated by the extensor hoods.
+
+
+
+
+
+Adduction	Adduction Abduction	Abduction
+
+
+
+
+
+
+
+Insertion into dorsal hood
+
+Insertion into base of proximal phalanx
+
+
+
+
+
+
+
+
+First dorsal interosseous
+
+Radial artery
+
+
+
+
+
+
+Fig. 7.104  Dorsal interossei (palmar view), right hand.
+
+
+Insertion into dorsal expansion
+
+
+
+
+
+
+
+
+
+
+
+
+First palmar interosseous (rudimentary: when present is often considered part of either adductor pollicis or flexor pollicis brevis)
+
+
+Fig. 7.105  Palmar interossei (palmar view), right hand.	795
+Upper Limb
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Transverse head of adductor pollicis
+
+
+
+
+
+
+
+
+
+
+Radial artery (deep palmar arch)
+Sesamoid bone
+
+
+Oblique head of adductor pollicis
+
+
+
+
+
+
+
+
+
+
+Fig. 7.106  Adductor pollicis, right hand.
+
+
+
+
+
+
+
+
+
+796
+Regional Anatomy  •  Hand	7
+
+
+
+
+
+
+
+
+
+
+Flexor digiti minimi brevis	Flexor pollicis brevis
+
+
+
+
+Three hypothenar muscles	Three thenar muscles
+
+
+
+
+
+Adductor pollicis and first palmar interosseous insert into medial side of extensor hood
+
+
+
+
+
+Extensor hood
+
+
+
+Opponens digiti minimi
+
+
+Abductor digiti minimi
+
+
+
+
+Deep branch of ulnar artery and nerve
+
+
+Flexor carpi ulnaris
+
+
+Flexor pollicis brevis and abductor pollicis brevis insert into lateral side of extensor hood
+
+Opponens pollicis
+
+Recurrent branch of median nerve
+
+
+Abductor pollicis brevis
+
+
+Median nerve
+
+
+
+Flexor retinaculum
+
+
+Fig. 7.107  Thenar and hypothenar muscles, right hand.
+
+
+
+
+
+
+
+
+
+797
+Upper Limb
+
+
+
+
+
+
+
+
+
+
+
+
+Deep transverse metacarpal ligament
+
+
+
+
+
+
+
+
+Attached to dorsal hood
+
+First and second lumbricals (unipennate)
+
+
+Flexor digitorum superficialis tendon (cut)
+
+
+Flexor digitorum profundus tendon
+
+
+
+
+
+Third and fourth lumbricals (bipennate)
+
+
+Flexor pollicis longus tendon
+
+
+
+Flexor retinaculum
+
+
+
+
+
+
+Fig. 7.108  Lumbrical muscles, right hand.
+
+
+
+
+
+
+
+
+
+
+798
+Regional Anatomy  •  Hand	7
+
+
+
+
+Dorsal interossei
+Dorsal interossei are the most dorsally situated of all of the intrinsic muscles and can be palpated through the skin on the dorsal aspect of the hand (Fig. 7.104). There are four bipennate dorsal interosseous muscles between, and
+
+■     The second and third dorsal interossei insert into the lateral  and  medial  sides,  respectively,  of  the  middle finger.
+■     The fourth dorsal interosseous muscle inserts into the medial side of the ring finger.
+
+attached  to,  the  shafts  of  adjacent  metacarpal  bones	In addition to generating flexion and extension move-
+
+(Fig. 7.104). Each muscle inserts both into the base of the proximal phalanx and into the extensor hood of its related digit.
+The tendons of the dorsal interossei pass dorsal to the deep transverse metacarpal ligaments:
+
+ments of  the fingers through their attachments to the extensor hoods, the dorsal interossei are the major abduc-tors of the index, middle, and ring fingers, at the metacar-pophalangeal joints (Table 7.15).
+The middle finger can abduct medially and laterally with respect to the long axis of  the middle finger and
+
+
+
+■     The first dorsal interosseous muscle is the largest and inserts into the lateral side of the index finger.
+
+consequently has a dorsal interosseous muscle on each side. The thumb and little finger have their own abductors
+
+
+
+
+Table 7.15    Intrinsic muscles of the hand (spinal segments indicated in bold are the major segments innervating the muscle)
+
+
+Muscle Palmaris brevis
+
+Dorsal interossei (four muscles)
+
+Palmar interossei (three or four muscles)
+
+Adductor pollicis
+
+
+Lumbricals (four muscles)
+
+
+
+THENAR MUSCLES Opponens pollicis
+
+Abductor pollicis brevis
+
+Flexor pollicis brevis
+
+Origin
+Palmar aponeurosis and flexor retinaculum
+Adjacent sides of metacarpals
+
+
+Sides of metacarpals
+
+
+
+Transverse head—metacarpal III; oblique head—capitate and bases of metacarpals II and III
+Tendons of flexor digitorum profundus
+
+
+
+
+Tubercle of trapezium and flexor retinaculum
+Tubercles of scaphoid and trapezium and adjacent flexor retinaculum
+Tubercle of the trapezium and flexor retinaculum
+
+Insertion
+Dermis of skin on the medial margin of the hand
+Extensor hood and base of proximal phalanges of index, middle, and ring fingers
+Extensor hoods of the thumb, index, ring, and little fingers and the proximal phalanx of thumb
+Base of proximal phalanx and extensor hood of thumb
+
+Extensor hoods of index, ring, middle, and little fingers
+
+
+
+
+Lateral margin and adjacent palmar surface of metacarpal I
+Proximal phalanx and extensor hood of thumb
+
+Proximal phalanx of the thumb
+
+Innervation
+Superficial branch of the ulnar nerve (C8, T1)
+Deep branch of ulnar nerve (C8, T1)
+
+Deep branch of ulnar nerve (C8, T1)
+
+
+Deep branch of ulnar nerve (C8, T1)
+
+Medial two by the deep branch of the ulnar nerve; lateral two by digital branches of the median nerve
+
+Recurrent branch of median nerve (C8, T1)
+Recurrent branch of median nerve (C8, T1)
+
+Recurrent branch of median nerve (C8, T1)
+
+Function Improves grip
+
+Abduction of index, middle, and ring fingers at the metacarpophalangeal joints
+Adduction of the thumb, index, ring, and little fingers at the metacarpophalangeal joints
+
+Adducts thumb
+
+
+Flex metacarpophalangeal joints while extending interphalangeal joints
+
+
+
+Medially rotates thumb
+
+Abducts thumb at metacarpophalangeal joint
+
+Flexes thumb at metacarpophalangeal joint
+
+HYPOTHENAR MUSCLES
+
+Opponens digiti minimi
+Abductor digiti minimi
+
+Flexor digiti minimi brevis
+
+Hook of hamate and flexor retinaculum
+Pisiform, the pisohamate ligament, and tendon of flexor carpi ulnaris
+Hook of the hamate and flexor retinaculum
+
+Medial aspect of metacarpal V
+
+Proximal phalanx of little finger
+
+Proximal phalanx of little finger
+
+Deep branch of ulnar nerve (C8, T1)
+Deep branch of ulnar nerve (C8, T1)
+
+Deep branch of ulnar nerve (C8, T1)
+
+Laterally rotates metacarpal V
+
+Abducts little finger at metacarpophalangeal joint
+
+Flexes little finger at metacarpophalangeal joint
+
+
+
+799
+Upper Limb
+
+
+
+in the thenar and hypothenar muscle groups, respectively, and therefore do not have dorsal interossei.
+The radial artery passes between the two heads of the first dorsal interosseous muscle as it passes from the ana-tomical snuffbox on the posterolateral side of the wrist into the deep aspect of the palm.
+
+Palmar interossei
+The three (or four) palmar interossei are anterior to the dorsal interossei, and are unipennate muscles originating from the metacarpals of  the digits with which each is associated (Fig. 7.105).
+The first palmar interosseous muscle is rudimentary and often considered part of either the adductor pollicis or the flexor pollicis brevis. When present, it originates from the medial side of  the palmar surface of  metacarpal I and inserts into both the base of the proximal phalanx of the thumb and into the extensor hood. A sesamoid bone often occurs in the tendon attached to the base of  the phalanx.
+The  second  palmar  interosseous  muscle  originates from  the  medial  surface  of  metacarpal  II  and  inserts into the medial side of  the extensor hood of  the index finger.
+The third and fourth palmar interossei originate from the lateral surfaces of metacarpals IV and V and insert into the lateral sides of the respective extensor hoods.
+Like the tendons of the dorsal interossei, the tendons of the palmar interossei pass dorsal to the deep transverse metacarpal ligaments.
+The palmar interossei adduct the thumb, index, ring, and little fingers with respect to a long axis through the middle finger. The movements occur at the metacarpopha-langeal joints. Because the muscles insert into the extensor hoods, they also produce complex flexion and extension movements of the digits (Table 7.15).
+
+Adductor pollicis
+The  adductor  pollicis  is  a  large  triangular  muscle anterior to the plane of the interossei that crosses the palm (Fig. 7.106). It originates as two heads:
+
+The radial artery passes anteriorly and medially between the two heads of the muscle to enter the deep plane of the palm and form the deep palmar arch.
+The adductor pollicis is a powerful adductor of  the thumb and opposes the thumb to the rest of the digits in gripping (Table 7.15).
+
+Thenar muscles
+The three thenar muscles (the opponens pollicis, flexor pollicis brevis, and abductor pollicis brevis muscles) are associated with opposition of the thumb to the fingers and with delicate movements of the thumb (Fig. 7.107) and are responsible for the prominent swelling (thenar emi-nence) on the lateral side of the palm at the base of the thumb.
+The thenar muscles are innervated by the recurrent branch of the median nerve.
+
+Opponens pollicis
+The opponens pollicis muscle is the largest of the thenar muscles and lies deep to the other two (Fig. 7.107). Origi-nating from the tubercle of the trapezium and the adjacent flexor retinaculum, it inserts along the entire length of the lateral  margin  and  adjacent  lateral  palmar  surface  of metacarpal I.
+The  opponens  pollicis  rotates  and  flexes  metacarpal I on the trapezium, so bringing the pad of the thumb into a position facing the pads of the fingers (Table 7.15).
+
+Abductor pollicis brevis
+The abductor pollicis brevis muscle overlies the oppo-nens pollicis and is proximal to the flexor pollicis brevis muscle (Fig. 7.107). It originates from the tubercles of the scaphoid and trapezium and from the adjacent flexor reti-naculum, and inserts into the lateral side of the base of the proximal phalanx of  the thumb and into the extensor hood.
+The abductor pollicis brevis abducts the thumb, princi-pally at the metacarpophalangeal joint. Its action is most apparent when the thumb is maximally abducted and the proximal phalanx is moved out of line with the long axis
+
+
+■     a transverse head from the anterior aspect of the shaft of metacarpal III, and
+■     an oblique head, from the capitate and adjacent bases of metacarpals II and III.
+
+The two heads converge laterally to form a tendon,
+
+of the metacarpal bone (Table 7.15).
+
+Flexor pollicis brevis
+The flexor pollicis brevis muscle is distal to the abductor pollicis brevis (Fig. 7.107). It originates mainly from the tubercle of the trapezium and adjacent flexor retinaculum, but it may also have deeper attachments to other carpal
+
+
+
+which often contains a sesamoid bone, that inserts into both the medial side of the base of the proximal phalanx of the thumb and into the extensor hood.
+800
+
+bones and associated ligaments. It inserts into the lateral side of the base of the proximal phalanx of the thumb. The tendon often contains a sesamoid bone.
+Regional Anatomy  •  Hand	7
+
+
+
+The flexor pollicis brevis flexes the metacarpophalangeal joint of the thumb (Table 7.15).
+
+Hypothenar muscles
+The  hypothenar  muscles  (the  opponens  digiti  minimi, abductor digiti minimi, and flexor digiti minimi brevis) contribute to the swelling (hypothenar eminence) on the medial side of the palm at the base of the little finger
+
+The flexor digiti minimi brevis flexes the metacarpopha-langeal joint.
+
+Lumbrical muscles
+There are four lumbrical (worm-like) muscles, each of which is associated with one of the fingers. The muscles originate from the tendons of the flexor digitorum profun-dus in the palm:
+
+
+
+(Fig. 7.107). The hypothenar muscles are similar to the thenar muscles in name and in organization.
+Unlike the thenar muscles, the hypothenar muscles are innervated by the deep branch of the ulnar nerve and not by the recurrent branch of the median nerve.
+
+Opponens digiti minimi
+The opponens digiti minimi muscle lies deep to the other two hypothenar muscles (Fig. 7.107). It originates from the hook of the hamate and from the adjacent flexor reti-naculum and it inserts into the medial margin and palmar
+
+
+■     The medial two lumbricals are bipennate and originate from the flexor digitorum profundus tendons associated with the middle and ring fingers and the ring and little fingers, respectively.
+■     The  lateral  two  lumbricals  are  unipennate  muscles, originating   from   the   flexor   digitorum   profundus tendons associated with the index and middle fingers, respectively.
+
+The lumbricals pass dorsally around the lateral side of
+
+
+
+surface of metacarpal V. Its base is penetrated by the deep branches of the ulnar nerve and ulnar artery.
+The opponens digiti minimi rotates metacarpal V toward the palm; however, because of  the simple shape of  the carpometacarpal joint and the presence of a deep trans-verse metacarpal ligament, which attaches the head of metacarpal V to that of the ring finger, the movement is much less dramatic than that of the thumb (Table 7.15).
+
+Abductor digiti minimi
+The abductor digiti minimi muscle overlies the opponens digiti minimi (Fig. 7.107). It originates from the pisiform bone, the pisohamate ligament, and the tendon of  the flexor carpi ulnaris, and inserts into the medial side of the base of the proximal phalanx of the little finger and into the extensor hood.
+The abductor digiti minimi is the principal abductor of the little finger (Table 7.15).
+
+Flexor digiti minimi brevis
+The flexor digiti minimi brevis muscle is lateral to the
+
+each finger, and insert into the extensor hood (Fig. 7.108). The tendons of the muscles are anterior to the deep trans-verse metacarpal ligaments.
+The  lumbricals  are  unique  because  they  link  flexor tendons with extensor tendons. Through their insertion into the extensor hoods, they participate in flexing the metacarpophalangeal joints and extending the interpha-langeal joints.
+The  medial  two  lumbricals  are  innervated  by  the deep branch of the ulnar nerve; the lateral two lumbricals are innervated by digital branches of  the median nerve (Table 7.15).
+
+
+Arteries and veins
+The blood supply to the hand is by the radial and ulnar arteries, which form two interconnected vascular arches (superficial and deep) in the palm (Fig. 7.109). Vessels to the digits, muscles, and joints originate from the two arches and the parent arteries:
+
+
+
+abductor  digiti  minimi  (Fig.  7.107).  It  originates  from the hook of the hamate bone and the adjacent flexor reti-naculum  and  inserts  with  the  abductor  digiti  minimi muscle into the medial side of  the base of  the proximal phalanx of the little finger.
+
+■     The radial artery contributes substantially to the supply of the thumb and the lateral side of the index finger.
+
+
+
+
+
+
+
+801
+Upper Limb
+
+
+
+
+
+
+
+
+
+
+
+
+
+Mainly ulnar artery
+
+
+
+Mainly radial artery
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Superficial palmar arch
+
+
+
+
+
+Deep palmar arch
+
+
+
+Ulnar artery	Radial artery
+
+
+
+
+
+Fig. 7.109  Arterial supply of the right hand.
+
+
+
+
+
+
+
+
+
+
+802
+Regional Anatomy  •  Hand	7
+
+
+■     The remaining digits and the medial side of the index	Branches from the superficial palmar arch include:
+
+finger are supplied mainly by the ulnar artery.
+
+Ulnar artery and superficial palmar arch
+The ulnar artery and ulnar nerve enter the hand on the medial side of the wrist (Fig. 7.110). The vessel lies between the  palmaris  brevis  and  the  flexor  retinaculum  and  is lateral to the ulnar nerve and the pisiform bone. Distally, the ulnar artery is medial to the hook of the hamate bone and then swings laterally across the palm, forming the superficial palmar arch, which is superficial to the long flexor tendons of  the digits and just deep to the palmar
+
+
+■     a palmar digital artery to the medial side of the little finger, and
+■     three large, common palmar digital arteries, which ultimately provide the principal blood supply to the lateral side of the little finger, both sides of the ring and middle fingers, and the medial side of the index finger (Fig.  7.110);  they  are  joined  by  palmar  metacarpal arteries from the deep palmar arch before bifurcating into the proper palmar digital arteries, which enter the fingers.
+
+
+
+aponeurosis. On the lateral side of the palm, the arch com-municates with a palmar branch of the radial artery.
+One branch of the ulnar artery in the hand is the deep palmar branch (Figs. 7.109 and 7.110), which arises from the medial aspect of the ulnar artery, just distal to the pisiform,  and  penetrates  the  origin  of  the  hypothenar muscles. It curves medially around the hook of the hamate to access the deep plane of the palm and to anastomose with the deep palmar arch derived from the radial artery.
+
+
+Radial artery and deep palmar arch
+The radial artery curves around the lateral side of the wrist and passes over the floor of the anatomical snuffbox and into the deep plane of the palm by penetrating anteri-orly through the back of the hand (Figs. 7.109 and 7.111). It passes between the two heads of the first dorsal interos-seous muscle and then between the two heads of  the
+
+
+
+
+
+Mainly ulnar artery
+
+
+
+
+
+Proper palmar digital arteries
+
+
+Palmar metacarpal artery
+
+
+Common palmar digital arteries
+
+
+
+Palmar digital artery
+
+
+Superficial palmar arch
+
+
+
+
+
+
+
+
+
+Fig. 7.110  Superficial palmar arch, right hand.
+
+Deep palmar artery
+
+
+Ulnar artery
+Ulnar nerve
+
+
+Thenar muscles
+
+
+
+Radial artery
+
+
+803
+Upper Limb
+
+
+
+adductor pollicis to access the deep plane of the palm and form the deep palmar arch.
+The deep palmar arch passes medially through the palm between the metacarpal bones and the long flexor tendons of the digits. On the medial side of the palm, it communicates with the deep palmar branch of the ulnar artery (Figs. 7.109 and 7.111).
+
+three  dorsal  metacarpal  arteries,  which  subse-quently divide to become small dorsal digital arteries, which enter the fingers; and
+■     the first dorsal metacarpal artery, which supplies adjacent sides of the index finger and thumb.
+
+Two  vessels,  the  princeps  pollicis  artery  and  the
+
+
+
+Before penetrating the back of  the hand, the radial artery gives rise to two vessels:
+
+radialis indicis artery, arise from the radial artery in the plane between the first dorsal interosseous and adductor pollicis. The princeps pollicis artery is the major blood
+
+
+
+■     a dorsal carpal branch, which passes medially as the dorsal carpal arch, across the wrist and gives rise to
+
+supply to the thumb, and the radialis indicis artery supplies the lateral side of the index finger.
+
+
+
+
+
+
+
+
+
+
+
+Mainly radial artery
+
+
+
+
+
+
+
+Radialis indicis artery
+
+
+
+Dorsal digital arteries
+
+
+Dorsal branches of proper palmar digital arteries
+
+
+
+
+
+
+
+Palmar metacarpal arteries
+Perforating artery
+
+Deep branch of ulnar artery
+
+
+Ulnar artery
+
+Ulnar nerve
+
+Dorsal digital arteries
+
+Dorsal interossei
+
+Princeps pollicis artery
+
+First dorsal interosseous muscle
+Adductor	Fir First dorsal
+st dorsal
+metacarpal
+arte
+pollicis	metacarpal ry
+muscle	artery
+Extensor carpi Deep palmar arch	radialis longus
+Dorsal caRadial artery in anatomical snuffbox
+rpal
+network
+Dorsal view
+Radial artery                            Extensor carpi radialis brevis
+Extensor retinaculum Extensor pollicis longus Abductor pollicis longus
+Extensor pollicis brevis
+
+
+
+Dorsal metacarpal arteries
+Dorsal
+Extensor
+carpal arch	digitorum Dorsal	tendons carpal branch
+(cut)
+of ulnar artery
+
+Posterior	Dorsal
+interosseous	metacarpal artery
+arteries
+Dorsal carpal arch
+Dorsal carpal branch of ulnar artery
+
+
+804	Fig. 7.111  Deep palmar arch, right hand.
+Regional Anatomy  •  Hand	7
+
+
+The deep palmar arch gives rise to:
+
+■     three palmar metacarpal arteries, which join the common palmar digital arteries from the superficial palmar arch; and
+■     three perforating branches, which pass posteriorly between the heads of origin of the dorsal interossei to anastomose with the dorsal metacarpal arteries from the dorsal carpal arch.
+
+
+
+In the clinic
+
+Allen’s test
+To test for adequate anastomoses between the radial and ulnar arteries, compress both the radial and ulnar arteries at the wrist, then release pressure from one or the other, and determine the filling pattern of the hand. If there is little connection between the deep and superficial palmar arteries, only the thumb and lateral side of the index finger will fill with blood (become red) when pressure on the radial artery alone is released.
+
+
+
+
+
+
+
+Anatomical snuffbox
+
+
+Cephalic vein
+
+
+
+
+
+Dorsal
+venous network
+
+
+
+
+
+Basilic vein
+
+
+
+
+
+Veins
+As generally found in the upper limb, the hand contains interconnected networks of deep and superficial veins. The deep veins follow the arteries; the superficial veins drain into a dorsal venous network on the back of the hand over the metacarpal bones (Fig. 7.112).
+The cephalic vein originates from the lateral side of the dorsal venous network and passes over the anatomical snuffbox into the forearm.
+The basilic vein originates from the medial side of the dorsal venous network and passes into the dorsomedial aspect of the forearm.
+
+
+In the clinic
+
+Venipuncture
+In many patients, venous access is necessary for obtaining blood for laboratory testing and administering fluid and intravenous drugs. The ideal sites for venous access are typically in the cubital fossa and in the cephalic vein adjacent to the anatomical snuffbox. The veins are simply distended by use of a tourniquet. A tourniquet should be applied enough to allow the veins to become prominent. For straightforward blood tests the antecubital vein is usually the preferred site, and although it may not always be visible, it is easily palpated. The cephalic vein is generally the preferred site for a short-term intravenous cannula.
+
+
+Fig. 7.112  Dorsal venous arch of the right hand.
+
+
+Nerves
+The hand is supplied by the ulnar, median, and radial nerves (Figs. 7.113 to 7.115). All three nerves contribute to cutaneous or general sensory innervation. The ulnar nerve innervates all intrinsic muscles of the hand except for the three thenar muscles and the two lateral lumbricals, which are innervated by the median nerve. The radial nerve only innervates skin on the dorsolateral side of the hand.
+
+Ulnar nerve
+The ulnar nerve enters the hand lateral to the pisiform and posteromedially to the ulnar artery (Fig. 7.113). Immedi-ately distal to the pisiform, it divides into a deep branch, which is mainly motor, and a superficial branch, which is mainly sensory.
+The deep branch of the ulnar nerve passes with the deep branch of the ulnar artery (Fig. 7.113). It penetrates and supplies the hypothenar muscles to reach the deep aspect of the palm, arches laterally across the palm, deep to the long flexors of the digits, and supplies the interossei, the adductor pollicis, and the two medial lumbricals. In addition, the deep branch of the ulnar nerve contributes
+small articular branches to the wrist joint.	805
+Upper Limb
+
+
+
+
+
+
+
+
+Area of distribution of superficial branch of ulnar nerve in hand
+
+
+Palmar branch of ulnar nerve from forearm
+
+
+
+
+Palmar view
+
+Medial two lumbrical muscles
+
+
+
+
+
+
+Deep branch (of ulnar nerve)
+
+
+Ulnar nerve
+
+Superficial branch (of ulnar nerve)
+
+
+
+Ulnar artery
+
+Dorsal branch of ulnar nerve from forearm
+
+
+Dorsal view
+
+
+Fig. 7.113  Ulnar nerve in the right hand.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+806
+Regional Anatomy  •  Hand	7
+
+
+
+In the clinic
+
+Ulnar nerve injury
+The ulnar nerve is most commonly injured at two sites: the elbow and the wrist.
+
+■     At the elbow, the nerve lies posterior to the medial epicondyle.
+■     At the wrist, the ulnar nerve passes superficial to the flexor retinaculum and lies lateral to the pisiform bone.
+
+Ulnar nerve lesions are characterized by “clawing” of the hand, in which the metacarpophalangeal joints of the fingers are hyperextended and the interphalangeal joints are flexed because the function of most of the intrinsic muscles of the hand is lost (Fig. 7.114).
+Clawing is most pronounced in the medial fingers
+
+
+
+because the function of all intrinsic muscles of these digits is lost while in the lateral two digits, the lumbricals are innervated by the median nerve. Function of the adductor pollicis muscle is also lost.
+In lesions of the ulnar nerve at the elbow, function of the flexor carpi ulnaris muscle and flexor digitorum profundus to the medial two digits is lost as well. Clawing of the hand, particularly of the little and ring fingers, is worse with lesions of the ulnar nerve at the wrist than at the elbow because interruption of the nerve at the elbow paralyzes the ulnar half of the flexor digitorum profundus, which leads to lack of flexion at the distal interphalangeal joints in these fingers.
+Ulnar nerve lesions at the elbow and wrist result in impaired sensory innervation on the palmar aspect of the medial one and one-half digits.
+Damage to the ulnar nerve at the wrist or at a site proximal to the wrist can be distinguished by evaluating the status of function of the dorsal branch (cutaneous) of the ulnar nerve, which originates in distal regions of the forearm. This branch innervates skin over the dorsal surface of the hand on the medial side.
+
+
+
+
+
+Fig. 7.114  Typical appearance of a “clawed hand” due to a lesion of the ulnar nerve.
+
+
+
+
+
+
+
+As the deep branch of the ulnar nerve passes across the palm,  it  lies  in  a  fibro-osseous  tunnel  (Guyon’s  canal) between the hook of the hamate and the flexor tendons. Occasionally, small outpouchings of  synovial membrane (ganglia) from the joints of the carpus compress the nerve within this canal, producing sensory and motor symptoms.
+
+The superficial branch of the ulnar nerve innervates the palmaris brevis muscle and continues across the palm to supply skin on the palmar surface of the little finger and the medial half of the ring finger (Fig. 7.113).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+807
+Upper Limb
+
+
+
+
+Median nerve
+The median nerve is the most important sensory nerve in the hand because it innervates skin on the thumb, index and middle fingers, and lateral side of  the ring finger (Fig. 7.115). The nervous system, using touch, gathers information about the environment from this area, particu-larly from the skin on the thumb and index finger. In addition, sensory information from the lateral three and one-half digits enables the fingers to be positioned with the appropriate amount of force when using precision grip.
+The median nerve also innervates the thenar muscles that are responsible for opposition of  the thumb to the other digits.
+The median nerve enters the hand by passing through the carpal tunnel and divides into a recurrent branch and palmar digital branches (Fig. 7.115).
+
+The recurrent branch of the median nerve innervates the three thenar muscles. Originating from the lateral side of the median nerve near the distal margin of the flexor retinaculum, it curves around the margin of the retinacu-lum and passes proximally over the flexor pollicis brevis muscle. The recurrent branch then passes between the flexor pollicis brevis and abductor pollicis brevis to end in the opponens pollicis.
+The palmar digital nerves cross the palm deep to the palmar aponeurosis and the superficial palmar arch and enter the digits. They innervate skin on the palmar surfaces of  the lateral three and one-half  digits and cutaneous regions over the dorsal aspects of the distal phalanges (nail beds) of  the same digits. In addition to skin, the digital nerves supply the lateral two lumbrical muscles.
+
+
+
+
+
+
+
+
+
+
+
+Palmar branch of median nerve from forearm
+
+
+
+
+
+Palmar view
+
+
+Lateral two lumbrical muscles
+
+
+Digital nerves
+
+
+
+
+Palmar branch (of median nerve)
+
+
+Median nerve
+
+Flexor pollicis brevis
+
+Abductor pollicis brevis
+
+Recurrent branch (of median nerve)
+
+
+
+
+Dorsal view
+
+808	Fig. 7.115  Median nerve in the right hand.
+Regional Anatomy  •  Hand	7
+
+
+
+
+Superficial branch of the radial nerve
+The only part of the radial nerve that enters the hand is the superficial branch (Fig. 7.116). It enters the hand by passing over the anatomical snuffbox on the dorsolateral side of the wrist. Terminal branches of the nerve can be
+
+
+
+In the clinic
+
+Radial nerve injury
+Around the elbow joint the radial nerve divides into its two terminal branches—the superficial branch and the deep branch.
+The most common radial nerve injury is damage to the nerve in the radial groove of the humerus, which produces a global paralysis of the muscles of the posterior compartment, resulting in wrist drop. Radial nerve damage can result from fracture of the shaft of the humerus as the radial nerve spirals around in the radial groove. The typical injury produces reduction of sensation in the cutaneous distribution,
+
+palpated or “rolled” against the tendon of  the extensor pollicis longus as they cross the anatomical snuffbox.
+The superficial branch of  the radial nerve innervates skin over the dorsolateral aspect of the palm and the dorsal aspects of the lateral three and one-half digits distally to approximately the terminal interphalangeal joints.
+
+
+
+
+
+predominantly over the posterior aspect of the hand. Severing the posterior interosseous nerve (continuation of deep branch of radial nerve) may paralyze the muscles of the posterior compartment of the forearm, but the nerve supply is variable. Typically, the patient may not be able to extend the fingers.
+The distal branches of the superficial branch of the radial nerve can be readily palpated as “cords” passing over the tendon of the extensor pollicis longus in the anatomical snuffbox. Damage to these branches is of little consequence because they supply only a small area of skin.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Superficial branch (of radial nerve)
+
+Anatomical snuffbox
+
+Palmar view	Dorsal view
+
+
+Fig. 7.116  Radial nerve in the right hand.
+
+
+
+
+
+
+
+
+
+
+
+809
+Upper Limb
+
+
+
+
+Surface anatomy Upper limb surface anatomy
+Tendons, muscles, and bony landmarks in the upper limb are used to locate major arteries, veins, and nerves. Asking patients to maneuver their upper limbs in specific ways is essential for performing neurological examinations.
+
+
+
+the scapula are deep to soft tissue and are not readily palpable. The  supraspinatus  and  infraspinatus  muscles can be palpated above and below the spine, respectively (Fig. 7.117).
+The  trapezius  muscle  is  responsible  for  the  smooth contour of the lateral side of the neck and over the superior
+
+
+
+
+■     Tendons are used to test reflexes associated with specific spinal cord segments.
+■     Vessels are used clinically as points of  entry into the vascular system (for collecting blood and administering pharmaceuticals and nutrients), and for taking blood pressure and pulses.
+■     Nerves can become entrapped or be damaged in regions where they are related to bone or pass through confined spaces.
+
+aspect of the shoulder.
+The deltoid muscles form the muscular eminence infe-rior to the acromion and around the glenohumeral joint. The axillary nerve passes posteriorly around the surgical neck of the humerus deep to the deltoid muscle.
+The latissimus dorsi muscle forms much of the muscle mass underlying the posterior axillary skin fold extending obliquely upward from the trunk to the arm. The teres major muscle passes from the inferior angle of the scapula to the upper humerus and contributes to this posterior
+
+Bony landmarks and muscles of the posterior	axillary skin fold laterally. scapular region
+
+The medial border, inferior angle, and part of the lateral border of the scapula can be palpated on a patient, as can the spine and acromion. The superior border and angle of
+
+
+
+
+Supraspinatus muscle
+
+Spine of scapula	Trapezius muscle
+
+Acromion
+
+Deltoid muscle
+
+
+
+Infraspinatus muscle
+
+Teres minor muscle
+
+Axillary nerve
+
+Teres major muscle
+
+
+
+Posterior axillary skin fold
+
+Latissimus dorsi muscle
+
+
+
+
+
+
+Fig. 7.117  Bony landmarks and muscles of the posterior scapular region. Posterior view of shoulder and back.
+
+
+
+810
+Surface Anatomy  •  Visualizing the Axilla and Locating Contents and Related Structures	7
+
+
+
+
+Visualizing the axilla and locating contents and related structures
+
+The axillary inlet and outlet and walls of the axilla can be established using skin folds and palpable bony landmarks (Fig. 7.118).
+
+immediately below the lateral third of the clavicle and deep to the medial margin of the deltoid muscle.
+■     The inferior margin of the anterior axillary wall is the anterior  axillary  skin  fold,  which  overlies  the  lower margin of the pectoralis major muscle.
+■     The inferior margin of the posterior axillary wall is the posterior axillary skin fold, which overlies the margins
+
+
+
+■     The anterior margin of the axillary inlet is the clavicle, which  can  be  palpated  along  its  entire  length. The lateral limit of  the axillary inlet is approximated by
+
+of the teres major muscle laterally and latissimus dorsi muscle medially.
+■     The medial wall of the axilla is the upper part of the
+
+the  tip  of  the  coracoid  process,  which  is  palpable	serratus anterior muscle overlying the thoracic wall.
+
+
+Clavicle Coracoid process
+Humerus
+
+
+Anterior wall Lateral wall
+Medial wall
+
+Posterior wall
+
+
+
+
+
+
+Anterior axillary skin fold
+
+
+Anterior axillary skin fold
+
+
+
+Opening of axilla into arm
+
+
+
+
+
+
+
+
+
+Posterior axillary skin fold
+
+A	B	Floor of axilla
+
+
+Pectoralis major muscle
+
+Axilla	Clavipectoral triangle
+Neurovascular bundle	Deltoid muscle
+
+Cephalic vein
+
+
+
+
+
+Serratus anterior muscle
+
+Long thoracic nerve
+
+
+C	D
+
+Fig. 7.118  Visualizing the axilla and locating its contents and related structures. A. Anterior shoulder showing folds and walls of the axilla.
+B. Anterior shoulder showing outlet and floor of the axilla. C. Anterior view showing the axillary neurovascular bundle and long thoracic nerve.
+D. Anterior view of the shoulder showing the clavipectoral triangle with the cephalic vein.	811
+Upper Limb
+
+
+
+The long thoracic nerve passes vertically out of  the axilla  and  down  the  lateral  surface  of  the  serratus anterior muscle in a position just anterior to the poste-rior axillary skin fold.
+■     The lateral boundary of the axilla is the humerus.
+■     The floor of the axilla is the dome of skin between the posterior and anterior axillary skin folds.
+
+Major vessels, nerves, and lymphatics travel between
+
+a hand into this dome of skin and pressing laterally against the humerus.
+The cephalic vein travels in superficial fascia in the cleft between the deltoid muscle and the pectoralis major muscle and penetrates deep fascia in the clavipectoral triangle to join with the axillary vein.
+
+
+Locating the brachial artery in the arm
+
+
+
+the upper limb and the trunk by passing through the axilla. The axillary artery, axillary vein, and components of the brachial plexus pass through the axilla and into the arm by traveling lateral to the dome of skin that forms the floor. This neurovascular bundle can be palpated by placing
+
+The brachial artery is on the medial side of the arm in the cleft between the biceps brachii and triceps brachii muscles (Fig. 7.119). The median nerve courses with the brachial artery, whereas the ulnar nerve deviates posteriorly from the vessel in distal regions.
+
+
+
+
+
+
+Brachial artery
+
+Median nerve
+
+
+
+
+
+
+
+
+Ulnar nerve
+
+
+
+
+Fig. 7.119  Locating the brachial artery in the right arm (medial view of arm with brachial artery, median nerve, and ulnar nerve).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+812
+Surface Anatomy  •  Cubital Fossa (Anterior View)	7
+
+
+
+
+The triceps brachii tendon and position of the radial nerve
+
+The triceps brachii muscle forms the soft tissue mass pos-terior to the humerus, and the tendon inserts onto the olecranon  of  the  ulna,  which  is  readily  palpable  and forms the bony protuberance at the “tip” of  the elbow (Fig. 7.120).
+The brachioradialis muscle is also visible as a muscular bulge on the lateral aspect of  the arm. It is particularly prominent when the forearm is half pronated, flexed at the elbow against resistance, and viewed anteriorly.
+The radial nerve in the distal arm emerges from behind the humerus to lie deep to the brachioradialis muscle.
+
+
+Cubital fossa (anterior view)
+The cubital fossa lies anterior to the elbow joint and con-tains the biceps brachii tendon, the brachial artery, and the median nerve (Fig. 7.121).
+
+epicondyles of the humerus. The lateral and medial borders are  formed  by  the  brachioradialis  and  pronator  teres muscles, respectively. The margin of  the brachioradialis can be found by asking a subject to flex the semipronated forearm against resistance. The margin of  the pronator teres can be estimated by an oblique line extending between the medial epicondyle and the midpoint along the length of the lateral surface of the forearm. The approximate apex of the cubital fossa is where this line meets the margin of the brachioradialis muscle.
+Contents of the cubital fossa, from lateral to medial, are the tendon of the biceps brachii, the brachial artery, and the median nerve. The tendon of the biceps brachii is easily palpable. Often the cephalic, basilic, and median cubital veins are visible in the subcutaneous fascia overlying the cubital fossa.
+The ulnar nerve passes behind the medial epicondyle of  the  humerus  and  can  be  “rolled”  here  against  the bone.
+The radial nerve travels into the forearm deep to the
+
+The   base   of   the   cubital   fossa   is   an   imaginary	margin of the brachioradialis muscle anterior to the elbow
+
+line  between  the  readily  palpable  medial  and  lateral
+
+
+
+
+
+
+
+Triceps brachii muscle
+
+joint.
+
+
+
+
+
+
+
+Brachioradialis muscle
+
+
+
+
+
+
+
+
+
+Triceps brachii tendon
+
+
+Triceps brachii muscle	Brachioradialis muscle
+
+
+
+
+
+
+
+
+Radial nerve	Triceps brachii tendon	Olecranon
+
+
+Fig. 7.120  Triceps brachii tendon and position of the radial nerve (posterior view of right arm).	813
+Upper Limb
+
+
+
+
+
+
+
+
+
+
+
+
+
+Humerus
+
+
+Cubital fossa
+Brachioradialis muscle
+
+
+
+
+
+
+
+
+A
+
+
+
+
+
+
+
+
+
+
+Biceps brachii tendon
+
+
+Cubital fossa
+
+Brachial artery
+
+Pronator teres muscle
+
+
+
+
+
+
+
+
+
+
+
+
+Cephalic vein
+Radial nerve
+Ulnar nerve
+
+Median cubital vein
+
+Cubital fossa
+
+
+Median nerve
+Basilic vein
+
+
+
+
+
+
+
+
+B	C
+
+
+Fig. 7.121  Cubital fossa (anterior view, right arm). A. Anterior view. B. Boundaries and contents. C. Showing radial and ulnar nerves, and veins.
+
+814
+Surface Anatomy  •  Identifying Tendons and Locating Major Vessels and Nerves in the Distal Forearm	7
+
+
+
+
+Identifying tendons and locating major vessels and nerves in the distal forearm
+
+Tendons that pass from the forearm into the hand are readily visible in the distal forearm and can be used as landmarks to locate major vessels and nerves.
+In the anterior aspect of the distal forearm, the tendons
+
+■     The tendon of  flexor carpi radialis is located approxi-mately at the junction between the lateral and middle thirds of an imaginary line drawn transversely across the distal forearm. The radial artery is immediately lateral to this tendon and this site is used for taking a radial pulse (Fig. 7.122A).
+■     The tendon of the flexor carpi ulnaris is easily palpated
+
+of   the  flexor  carpi  radialis,  flexor  carpi  ulnaris,  and	along the medial margin of  the forearm and inserts
+
+palmaris longus muscles can be easily located either by palpating or by asking a patient to flex the wrist against resistance.
+
+on the pisiform, which can also be palpated by following the tendon to the base of  the hypothenar eminence of the hand. The ulnar artery and ulnar nerve travel
+
+
+
+
+
+
+
+Flexor carpi radialis tendon
+
+Palmaris longus tendon
+
+Thenar eminence
+
+Radial artery
+
+Ulnar artery
+
+
+
+
+
+
+
+
+Ulnar nerve A	Flexor carpi ulnaris	Hypothenar eminence	Pisiform
+
+Extensor carpi radialis brevis tendon
+Extensor carpi radialis longus tendon
+
+Extensor carpi ulnaris tendon
+
+
+Extensor digitorum tendon
+
+
+C	Abductor pollicis longus tendon
+
+Extensor pollicis brevis tendon
+
+Anatomical snuffbox Extensor pollicis longus tendon
+Cephalic vein
+
+
+
+
+
+
+Radial artery
+
+Abductor pollicis longus tendon Extensor pollicis brevis tendon
+B	D
+
+Fig. 7.122  Identifying tendons and locating major vessels and nerves in the distal right forearm. A. Anterior distal forearm and wrist. B.
+Posterior distal forearm and wrist. C. Lateral view of posterior wrist and forearm. D. Anatomical snuffbox.	815
+Upper Limb
+
+
+
+through the distal forearm and into the hand under the lateral lip of the flexor carpi ulnaris tendon and lateral to the pisiform.
+■     The palmaris longus tendon may be absent, but when present, lies medial to the flexor carpi radialis tendon and is particularly prominent when the wrist is flexed against resistance. The median nerve is also medial to the flexor carpi radialis tendon and lies under the pal-maris longus tendon.
+■     The long tendons of the digits of the hand are deep to the median nerve and between the long flexors of the wrist. Their position can be visualized by rapidly and repeatedly flexing and extending the fingers from medial to lateral.
+■     In the posterior distal forearm and wrist, the tendons of the extensor digitorum (Fig. 7.122B) are in the midline and radiate into the index, middle, ring, and little fingers from the wrist.
+■     The distal ends of  the tendons of  the extensor carpi radialis longus and brevis muscles are on the lateral side of the wrist (Fig. 7.122C) and can be accentuated by making a tight fist and extending the wrist against resistance.
+■     The tendon of the extensor carpi ulnaris can be felt on the far medial side of the wrist between the distal end of the ulna and the wrist.
+■     Hyperextension and abduction of the thumb reveals the anatomical snuffbox (Fig. 7.122D). The medial margin of  this triangular area is the tendon of  the extensor pollicis longus, which swings around the dorsal tubercle of  the radius and then travels into the thumb. The lateral margin is formed by the tendons of the extensor
+
+
+Thenar eminence
+
+
+
+
+
+
+
+
+
+
+A
+
+
+
+
+
+Basilic vein
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+B
+
+
+
+
+
+
+
+
+
+
+
+
+Hypothenar eminence
+
+
+
+
+
+
+
+Cephalic vein
+
+Dorsal
+venous network
+
+pollicis brevis and abductor pollicis longus. The radial artery passes through the anatomical snuffbox when traveling laterally around the wrist to reach the back of the hand and penetrate the base of  the first dorsal interosseous muscle to access the deep aspect of  the palm of the hand. The pulse of the radial artery can be felt in the floor of the anatomical snuffbox in the relaxed wrist. The cephalic vein crosses the roof of the anatomi-cal  snuffbox,  and  cutaneous  branches  of  the  radial nerve can be felt by moving a finger back and forth along the tendon of the extensor pollicis longus muscle.
+
+
+Normal appearance of the hand
+In the resting position, the palm and digits of  the hand have a characteristic appearance. The fingers form a flexed arcade, with the little finger flexed the most and the index finger flexed the least (Fig. 7.123A). The pad of the thumb is positioned at a 90° angle to the pads of the fingers.
+816
+
+
+Fig. 7.123  Normal appearances of the right hand. A. Palmar view with the thenar and hypothenar eminences and finger arcade. B. Dorsal view with dorsal venous network.
+
+
+
+
+
+A thenar eminence occurs at the base of the thumb and is formed by the underlying thenar muscles. A similar hypothenar eminence occurs along the medial margin of the palm at the base of the little finger. The appearance of the thenar and hypothenar eminences, and the positions of the fingers change when the ulnar and median nerves are compromised.
+Major superficial veins of the upper limb begin in the hand from a dorsal venous network (Fig. 7.123B), which overlies the metacarpals. The basilic vein originates from the medial side of the network and the cephalic vein origi-nates from the lateral side.
+Surface Anatomy  •  Motor Function of the Median and Ulnar Nerves in the Hand	7
+
+
+
+
+Position of the flexor retinaculum and the recurrent branch of the median nerve
+
+The proximal margin of  the flexor retinaculum can be determined using two bony landmarks.
+
+The recurrent branch of the median nerve lies deep to the skin and deep fascia overlying the anterior margin of the thenar eminence near the midline of the palm.
+
+Motor function of the median and ulnar nerves in the hand
+
+
+
+■     The pisiform bone is readily palpable at the distal end of the flexor carpi ulnaris tendon.
+■     The tubercle of  the scaphoid can be palpated at the distal end of the flexor carpi radialis tendon as it enters the wrist (Fig. 7.124).
+
+An imaginary line between these two points marks the
+
+
+The ability to flex the metacarpophalangeal joints while at the same time extending the interphalangeal joints of the fingers is entirely dependent on the intrinsic muscles of the hand (Fig. 7.125A). These muscles are mainly inner-vated by the deep branch of the ulnar nerve, which carries fibers from spinal cord level (C8)T1.
+Adducting the fingers to grasp an object placed between
+
+
+
+proximal  margin  of  the  flexor  retinaculum. The  distal margin of the flexor retinaculum is approximately deep to the point where the anterior margin of  the thenar emi-nence meets the hypothenar eminence near the base of the palm.
+
+them is caused by the palmar interossei muscles, which are innervated by the deep branch of the ulnar nerve carrying fibers from spinal cord level (C8)T1.
+The ability to grasp an object between the pad of the thumb and the pad of one of the fingers depends on normal
+
+
+
+
+Thenar eminence
+
+Tubercle of the scaphoid
+
+
+Recurrent branch of the median nerve
+
+
+Flexor carpi radialis tendon
+
+
+
+Median nerve
+
+
+
+
+
+
+Fig. 7.124  Anterior view of left hand to show the position of the flexor retinaculum and recurrent branch of the median nerve.
+
+
+Flexor carpi ulnaris tendon
+
+Hypothenar eminence Pisiform
+Flexor retinaculum
+
+
+
+
+
+
+
+
+
+
+
+
+
+A	B	C
+
+Fig. 7.125  Motor function of the ulnar and median nerves in the hand. A. Flexing the metacarpophalangeal joints and extending the interphalangeal joints: the “ta-ta” position. B. Grasping an object between the fingers. C. Grasping an object between the pad of the thumb and pad of the index finger.
+
+817
+Upper Limb
+
+
+
+functioning of the thenar muscles, which are innervated by the recurrent branch of  the median nerve carrying fibers from spinal cord level C8(T1).
+
+Visualizing the positions of the superficial and deep palmar arches
+
+
+Pulse points
+Peripheral pulses can be felt at six locations in the upper limb (Fig. 7.127).
+
+■     Axillary pulse: axillary artery in the axilla lateral to the
+
+
+
+The positions of the superficial and deep palmar arches in the hand can be visualized using bony landmarks, muscle eminences, and skin creases (Fig. 7.126).
+
+apex of the dome of skin covering the floor of the axilla. ■     Brachial pulse in midarm: brachial artery on the medial
+side of the arm in the cleft between the biceps brachii and triceps brachii muscles. This is the position where a
+
+
+
+■     The superficial palmar arch begins as a continuation of the ulnar artery, which lies lateral to the pisiform bone at the wrist. The arch curves laterally across the palm anterior to the long flexor tendons in the hand. The arch reaches as high as the proximal transverse skin crease of the palm and terminates laterally by joining a vessel of  variable size, which crosses the thenar eminence from the radial artery in the distal forearm.
+■     The deep palmar arch originates on the lateral side of the palm deep to the long flexor tendons and between the proximal ends of  metacarpals I and II. It arches medially across the palm and terminates by joining the deep branch of the ulnar artery, which passes through the base of  the hypothenar muscles and between the pisiform and hook of the hamate. The deep palmar arch is more proximal in the hand than the superficial palmar arch and lies approximately one-half  of  the distance between the distal wrist crease and the proximal trans-verse skin crease of the palm.
+
+blood pressure cuff is placed.
+■     Brachial  pulse  in  the  cubital  fossa:  brachial  artery medial to the tendon of the biceps brachii muscle. This is the position where a stethoscope is placed to hear the pulse of the vessel when taking a blood pressure reading.
+■     Radial pulse in the distal forearm: radial artery immedi-ately lateral to the tendon of  the flexor carpi radialis muscle. This is the most common site for “taking a pulse.”
+■     Ulnar pulse in the distal forearm: ulnar artery immedi-ately under the lateral margin of the flexor carpi ulnaris tendon and proximal to the pisiform.
+■     Radial pulse in the anatomical snuffbox: radial artery as it crosses the lateral side of the wrist between the tendon of the extensor pollicis longus muscle and the tendons of  the  extensor  pollicis  brevis  and  abductor  pollicis longus muscles.
+
+
+
+
+
+
+Proximal transverse skin crease of palm
+Distal wrist crease
+
+Proximal wrist crease
+
+Radial artery
+
+
+
+
+Distal transverse skin crease of palm
+
+
+
+
+
+
+
+
+
+
+Ulnar artery
+Pisiform
+
+Superficial palmar arch
+Deep palmar arch
+Hook of hamate
+
+
+Fig. 7.126  Visualizing the positions of the superficial and deep palmar arches, left hand. The proximal transverse skin crease of the palm and distal wrist crease are labeled and the superficial and deep palmar arches shown in overlay. This also shows the position of the pisiform and the
+818	hook of the hamate.
+Surface Anatomy  •  Pulse Points	7
+
+
+
+
+
+
+
+
+
+
+
+
+Axillary pulse	Brachial pulse in midarm
+
+
+
+
+
+
+
+
+
+
+
+
+Brachial pulse in the cubital fossa
+
+
+Radial pulse in distal forearm
+
+
+
+
+
+
+
+
+
+Ulnar pulse in distal forearm A
+
+
+
+
+
+
+
+
+
+
+
+Radial pulse in the anatomical snuffbox
+
+
+
+
+B
+
+Fig. 7.127  Where to take peripheral artery pulses in the upper limb. A. Pulse points. B. Placement of blood pressure cuff and stethoscope.	819
+Upper Limb
+
+
+Clinical cases
+
+
+Case 1
+
+WINGED SCAPULA
+
+A 57-year-old woman underwent a right mastectomy for a breast cancer. The surgical note reported that all of the breast tissue had been removed, including the axillary process. In addition, the surgeon had dissected all lymph nodes within the axilla with their surrounding fat. The patient made an uneventful recovery.
+
+At the first follow-up appointment, the patient’s husband told the surgeon that she had now developed a bony “spike” on her back. The surgeon was intrigued and asked the patient to reveal this spike. At examination, the spike was the inferior angle of the scapula, which appeared to be sticking out posteriorly (“winged”). Raising the arms accentuated this structure.
+
+
+
+
+
+
+Case 2
+
+COMPLICATION OF A FRACTURED FIRST RIB
+
+A 25-year-old woman was involved in a motor vehicle accident and thrown from her motorcycle. When she was admitted to the emergency room, she was unconscious. A series of tests and investigations were performed, one of which included chest radiography. The attending physician noted a complex fracture of the first rib on the left.
+
+Many important structures that supply the upper limb pass over rib I.
+
+It is important to test the nerves that supply the arm and hand, although this is extremely difficult to do in an unconscious patient. However, some muscle reflexes can be determined using a tendon hammer. Also, it may be possible to test for pain reflexes in patients with altered consciousness levels. Palpation of the axillary artery, brachial artery, radial artery, and ulnar artery pulses is necessary because a fracture of the first rib can sever and denude the subclavian artery, which passes over it.
+
+
+
+The medial border of the scapula was accentuated and it was noted that there was some loss of bulk of the
+serratus anterior muscle, which attaches to the tip of the scapula.
+
+The nerve to this muscle was damaged.
+
+During the surgery on the axilla, the long thoracic nerve was damaged as it passed down the lateral thoracic wall on the external surface of the serratus anterior, just deep to the skin and subcutaneous fascia.
+
+Because the nerve was transected, it is unlikely that the patient will improve, but she was happy that she had an adequate explanation for the spike.
+
+
+
+
+
+
+
+
+
+A chest drain was immediately inserted because the lung had collapsed. The fractured first rib had damaged the visceral and parietal pleurae, allowing air from a torn lung to escape into the pleural cavity. The lung collapsed, and the pleural cavity filled with air, which impaired lung function.
+
+A tube was inserted between the ribs, and the air was sucked out to re-inflate the lung.
+
+The first rib is a deep structure at the base of the neck. It is not uncommon for ribs to be broken after minor injuries, including sports injuries. However, rib I, which lies at the base of the neck, is surrounded by muscles and soft tissues that provide it with considerable protection. Therefore a patient with a fracture of the first rib has undoubtedly been subjected to a considerable force, which usually occurs in a deceleration injury. Other injuries should always be sought and the patient should be managed with a high level of concern for deep neck and mediastinal injuries.
+
+
+
+
+
+
+
+
+
+820
+Clinical Cases  •  Case 3	7
+
+
+
+Case 3
+
+HOW TO EXAMINE THE HAND
+
+A resident was asked to carry out a clinical assessment of a patient’s hand. He examined the following:
+
+Musculoskeletal system
+The musculoskeletal system includes the bones, joints, muscles, and tendons. The resident looked for abnormalities and muscle wasting. Knowing which areas are wasted identifies the nerve that supplies them. She palpated the individual bones and palpated the scaphoid with the wrist in ulnar deviation. She examined the movement of joints because they may be restricted by joint disease or inability of muscular contraction.
+
+Circulation
+Palpation of both radial and ulnar pulses is necessary. The resident looked for capillary return to assess how well the hand was perfused.
+
+Examination of the nerves
+The three main nerves to the hand should be tested.
+
+Median nerve
+The median nerve innervates the skin on the palmar aspect of the lateral three and one-half digits, the dorsal aspect of the distal phalanx, half of the middle phalanges of the same fingers, and a variable amount on the radial side of the palm of the hand. Median nerve damage results in wasting of the
+
+
+
+thenar eminence, absence of abduction of the thumb, and absence of opposition of the thumb.
+
+Ulnar nerve
+The ulnar nerve innervates the skin of the anterior and posterior surfaces of the little finger and the ulnar side of the ring finger, the skin over the hypothenar eminence, and a similar strip of skin posteriorly. Sometimes the ulnar nerve innervates all the skin of the ring finger and the ulnar side of the middle finger.
+
+An ulnar nerve palsy results in wasting of the hypothenar eminence, absent flexion of the distal interphalangeal joints of the little and ring fingers, and absent abduction and adduction of the fingers. Adduction of the thumb also is affected.
+
+Radial nerve
+The radial nerve innervates a small area of skin over the lateral aspect of metacarpal I and the back of the first web space.
+
+The radial nerve also produces extension of the wrist and extension of the metacarpophalangeal and interphalangeal joints and of the digits.
+
+A very simple examination would include tests for the median nerve by opposition of the thumb, for the ulnar nerve by abduction and adduction of the digits, and for the radial nerve by extension of the wrist and fingers and feeling on the back of the first web space.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+821
+Clinical Cases  •  Case 5	7
+
+
+
+Case 4
+
+SHOULDER PROBLEM AFTER FALLING ON AN OUTSTRETCHED HAND
+
+A 45-year-old man came to his physician complaining of pain and weakness in his right shoulder. The pain began after a fall on his outstretched hand approximately 6 months previously. The patient recalled having some minor shoulder tenderness but no other specific symptoms. He was otherwise fit and well.
+
+On examination of the shoulder, there was marked wasting of the muscles in the supraspinous and infraspinous fossae. The patient found initiation of abduction difficult and there was a weakness of lateral rotation of the humerus.
+
+The wasted muscles were the supraspinatus and infraspinatus. The cause of the muscle wasting was disuse.
+
+Muscle atrophy (wasting) occurs through a variety of disorders. Disuse atrophy is one of the most common causes. Examples of disuse atrophy include the loss of muscle bulk after fracture immobilization in a plaster cast.
+
+
+
+
+
+
+Case 5
+
+BRACHIAL PLEXUS NERVE BLOCK
+
+A surgeon wished to carry out a complex procedure on a patient’s wrist, and asked the anesthesiologist whether the whole arm could be numbed while the patient was awake. Within 20 minutes the anesthesiologist had carried out the procedure after injecting 10 mL of local anesthetic into the axilla. The surgeon went ahead with the operation and
+the patient did not feel a thing.
+
+The anesthetic was injected into the axillary sheath.
+
+It would be almost impossible to anesthetize the wrist in the forearm because local anesthetic would have to be placed accurately around the ulnar, median, and radial nerves. Furthermore, all of the cutaneous branches of the forearm would also have to be anesthetized individually, which would take a considerable amount of time and probably produce subtotal anesthesia.
+
+The nerves of the upper limb originate from the brachial plexus, which surrounds the axillary artery within the axilla. Importantly, the axillary artery, axillary vein, and brachial
+
+
+
+The opposite effect can also be demonstrated—when muscles are overused they become bulkier (hypertrophy).
+
+The supraspinatus and infraspinatus muscles are supplied by the suprascapular nerve (C5, C6), which originates from the superior trunk of the brachial plexus. Given that only these muscles were involved, it is highly likely that the muscle atrophy is caused by denervation. Denervation may result from a direct nerve transection, nerve compression, or a pharmacological effect on the nerve.
+
+The typical site for compression of the suprascapular nerve is the suprascapular notch (foramen) on the superior margin of the scapula.
+
+The patient’s apparently minor injury damaged the fibrocartilaginous glenoid labrum, which allowed a cyst to form and pass along the superior border of the scapula to the suprascapular notch (foramen), where the cyst compressed the suprascapular nerve.
+
+Surgical excision of the damaged glenoid labrum and removal of the cyst improved the patient’s symptoms.
+
+
+
+
+
+
+
+
+plexus lie within the sleeve-like covering of fascia termed the axillary sheath. By injecting the anesthetic into the space enclosed by the axillary sheath, all of the nerves of the brachial plexus were paralyzed.
+
+It is possible with a patient’s arm abducted and externally rotated (palm behind the head) to easily palpate the axillary artery and therefore locate the position of the axillary sheath. Once the axillary artery has been identified, a small needle can be placed beside the vessel and local anesthetic can be injected on both sides of it. The local anesthetic tracks along the axillary sheath in this region. The brachial plexus surrounding the axillary artery is therefore completely anesthetized and an effective local anesthetic “block” is achieved.
+
+“Could there be any complications?” asks the patient.
+
+Potential complications are a direct needle spike of the branches of the brachial plexus, damage to the axillary artery, and inadvertent arterial injection of the local anesthetic. Fortunately, these are rare in skilled hands.
+
+
+
+
+821.e1
+Upper Limb
+
+
+
+Case 6
+
+MEDIAN NERVE COMPRESSION
+
+A 35-year-old woman comes to her physician complaining of tingling and numbness in the fingertips of the first, second, and third digits (thumb, index, and middle fingers). The symptoms were provoked by arm extension. Local anesthesia was also present around the base of the thenar eminence.
+
+The problem was diagnosed as median nerve compression.
+
+The median nerve is formed from the lateral and medial cords of the brachial plexus anterior to the axillary artery and passes into the arm anterior to the brachial artery. At the level of the elbow joint it sits medial to the brachial artery, both of which are medial to the tendon of the biceps. In the forearm the nerve courses through the anterior compartment and passes deep to the flexor retinaculum. It innervates most of the muscles of the forearm, the thenar muscles, the two lateral lumbricals, and the skin over the palmar surface of the lateral three and one-half digits and over the lateral side of the palm and the middle of the wrist.
+
+In this patient, the median nerve initially was believed to be trapped below the flexor retinaculum (carpal tunnel syndrome).
+
+Carpal tunnel syndrome is a common problem in young to middle-aged patients. Typically the nerve becomes compressed within the carpal tunnel. This syndrome may be associated with a number of medical conditions, such as thyroid disease and pregnancy. Occasionally a small ganglion or a tumor situated within the carpal tunnel can
+
+
+
+also compress the nerve. Other possibilities include tenosynovitis in patients with rheumatoid arthritis.
+
+Nerve conduction studies were performed to confirm the clinical findings. Nerve conduction studies are a series of tests that send small electrical impulses along the length of a variety of nerves in order to measure the speed at which the nerve conducts these pulses. The speed of the nerve pulse can be measured and is referred to as the latency. In our patient it was noted that the nerve had normal latency to the elbow joint; however, below the elbow joint there was increased latency.
+
+The nerve conduction studies indicated that the compression site was at the elbow joint.
+
+The clinical findings are not consistent with carpal tunnel syndrome. The clinician should have been alerted to this problem given that the patient experienced numbness over the thenar eminence of the hand. This clue indicates an understanding of the anatomy. Compression of the nerve within the carpal tunnel does not produce this numbness, because the small cutaneous branch that supplies this region is proximal to the flexor retinaculum.
+
+The nerve compromise was caused by the ligament of Struthers, which is an embryological remnant of the coracobrachialis muscle. It is an extremely rare finding. Occasionally it may ossify and cross the nerve, artery, and vein to produce compression in arm extension. Although this is very rare and unusual, it illustrates the complex course of the median nerve.
+
+
+
+
+
+
+Case 7
+
+IMMOBILIZING THE EXTENSOR DIGITORUM MUSCLE
+
+After a hard day’s studying, two medical students decided to meet for coffee. The more senior student said to the freshman that he would bet him $50 that he could not lift a matchbook with a finger. The freshman placed $50 on the table and the bet was on. The senior medical student told the freshman to make a fist and place it in a
+palm-downward position, so that the middle phalanges of the fingers were in direct contact with the bar counter. He was then told to extend his middle finger so that it stuck forward while maintaining the middle phalanges of the index finger, the ring finger, and the little finger on the bar surface.
+
+A matchbook was placed on top of the freshman’s middle fingernail and he was told to flip it. He couldn’t. He lost the $50.
+821.e2
+
+
+
+Extension of the index, middle, ring, and little fingers is performed by the extensor digitorum muscle.
+
+Placing the fist in a palm-down position on the table and pressing the middle phalanges onto the table effectively immobilizes the action of the extensor digitorum. The freshman was therefore unable to elevate his middle finger (which was sticking out). It is important to remember that if this same procedure is carried out leaving the index or little finger free to move, they do. This is because these two digits are extended not only by the extensor digitorum muscle but also by the extensor indicis muscle (index finger) and extensor digiti minimi muscle (little finger).
+Clinical Cases  •  Case 8	7
+
+
+
+Case 8
+
+TORN SUPRASPINATUS TENDON
+
+A 70-year-old woman came to an orthopedic surgeon with right shoulder pain and failure to initiate abduction of the shoulder. Further examination revealed loss of muscle bulk in the supraspinous fossa. The supraspinatus muscle was damaged.
+
+Abduction of the humerus at the glenohumeral joint is initiated by the supraspinatus muscle. After the shoulder has been abducted to 10°–15°, the deltoid muscle continues the movement. The patient was able to abduct her arm by lowering and tilting the glenohumeral joint inferiorly to enable the deltoid to obtain its mechanical advantage.
+
+The loss of muscle bulk in the supraspinous fossa suggested muscle atrophy.
+
+
+
+the shoulder, exposing the supraspinatus tendon for ultrasound scan examination. The ultrasound revealed a completely torn tendon with fluid in the subacromial subdeltoid bursa (eFig. 7.128). The patient underwent
+a surgical repair and made a good recovery.
+
+
+
+Deltoid muscle
+
+
+
+Muscle atrophy occurs when a muscle is not used. The orthopedic surgeon thought that there was a tear of the supraspinatus tendon beneath the acromion. If this was so, the muscle would atrophy.
+
+The diagnosis was confirmed by ultrasound scan.
+
+
+
+
+Head of humerus
+Tear in supraspinatus tendon
+
+
+
+
+Head of humerus
+Normal supraspinatus tendon
+
+
+
+The patient was seated on a stool and her right shoulder was uncovered. The patient’s hand was placed over her right buttock, a position that acts to externally rotate and extend
+
+
+eFig. 7.128  Ultrasound showing a completely torn supraspinatus tendon with fluid in the subacromial subdeltoid bursa.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+821.e3
+Upper Limb
+
+
+
+Case 9
+
+SHOULDER JOINT PROBLEM
+
+A 35-year-old baseball pitcher came to the clinic with a history of a recurrent dislocation of the shoulder (eFig. 7.129). An MRI scan was performed to assess the shoulder joint prior to any treatment.
+
+The MRI demonstrates the anatomical structures in multiple planes, allowing the physician to obtain an overview of the shoulder and to assess any intraarticular or extraarticular structures that may have been damaged and require surgical repair.
+
+The MRI demonstrated a divot in the posterosuperior aspect of the humeral head and a small fragment of bone and glenoid labrum that had become separated in the anteroinferior aspect of the glenoid cavity.
+
+Shoulder dislocation is not an uncommon problem and may occur as a “once-off” or with repetitive injury may be recurrent. Recurrent dislocations may be bilateral and symmetrical (a memory aid is “torn loose or born loose”).
+
+The MRI findings are typical for an anteroinferior dislocation, which is the most common type; moreover the MRI demonstrates the injuries that occur within the joint at the time of dislocation. These injuries include the abutment of the posterosuperior aspect of the humeral head on the anteroinferior aspect of the glenoid cavity. This type of injury, when recurrent, may avulse a small fragment of the glenoid labrum, and in some cases this may attach to a small fragment of bone (the Bankart lesion). When the shoulder is relocated, the integrity of the capsular attachment anteroinferiorly has been disrupted, potentially making the shoulder somewhat prone to further dislocation.
+
+An arthroscopic repair was performed.
+
+Arthroscopy of the shoulder is an established method for assessing the shoulder joint. Portals of entry are anterior and
+
+
+
+posterior and small holes in the capsule are made percutaneously. The shoulder joint is filled with saline, which distends it, allowing the arthroscope to move around the joint and inspect the joint surfaces, including the labrum. The labrum and its bony fragment were reattached and sutured using anchor sutures (somewhat similar to staples). The anterior aspect of the capsule was also tightened.
+
+The patient made an uneventful recovery.
+
+After the procedure the arm was held in internal rotation and remained adducted. Gentle exercise and physiotherapy were performed and the patient returned to playing baseball.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+eFig. 7.129  The radiograph, anteroposterior view, demonstrates an anteroinferior dislocation of the humeral head at the glenohumeral joint.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+821.e4
+This page intentionally left blank
+
+
+
+
+Meninges	861
+Cranial dura mater	861 Arachnoid mater      864 Pia mater	865
+Arrangement of meninges and spaces	865 Brain and its blood supply	867
+Brain	867
+Blood supply	868 Venous drainage      874
+Cranial nerves	883 Olfactory nerve [I]	885 Optic nerve [II]      885
+Oculomotor nerve [III]	886 Trochlear nerve [IV]      886 Trigeminal nerve [V]      887 Ophthalmic nerve [V1]	887 Maxillary nerve [V2]      887 Mandibular nerve [V3]      887 Abducent nerve [VI]      887 Facial nerve [VII]	887
+Vestibulocochlear nerve [VIII]	888 Glossopharyngeal nerve [IX]      888 Vagus nerve [X]	892
+Accessory nerve [XI]	892 Hypoglossal nerve [XII]      892
+Face	893
+Muscles	893 Parotid gland	900 Innervation      903 Vessels      905
+Scalp		911 Layers	911
+Innervation	913 Vessels	914
+Lymphatic drainage	915 Orbit	916
+Bony orbit	916 Eyelids      917
+Lacrimal apparatus	921 Fissures and foramina      923 Fascial specializations      924 Muscles	925
+Vessels	931 Innervation	932 Eyeball	936
+Ear	942
+External ear	943 Middle ear      947 Internal ear      954
+Temporal and infratemporal fossae	961 Bony framework	962 Temporomandibular joints	964 Masseter muscle	966
+Temporal fossa	967
+
+
+Infratemporal fossa	970 Pterygopalatine fossa      981
+Skeletal framework	982 Gateways	983
+Contents	983 Neck	989
+Fascia	989
+Superficial venous drainage	992 Anterior triangle of the neck      995 Posterior triangle of the neck      1012 Root of the neck	1019
+Pharynx	1029
+Skeletal framework	1030 Pharyngeal wall      1031 Fascia	1034
+Gaps in the pharyngeal wall and structures passing through them	1035
+Nasopharynx	1035 Oropharynx      1037 Laryngopharynx      1037 Tonsils	1037
+Vessels      1038 Nerves      1040
+Larynx	1041
+Laryngeal cartilages	1042 Extrinsic ligaments      1045 Intrinsic ligaments      1046 Laryngeal joints	1047 Cavity of the larynx	1048 Intrinsic muscles      1050 Function of the larynx      1053 Vessels	1055
+Nerves	1057 Nasal cavities      1058
+Lateral wall	1059 Regions      1060
+Innervation and blood supply	1061 Skeletal framework	1061
+External nose	1063 Paranasal sinuses	1063 Walls, floor, and roof      1065 Nares	1069
+Choanae	1070 Gateways      1071 Vessels      1071 Innervation      1074
+Oral cavity	1076
+Multiple nerves innervate the oral cavity	1077 Skeletal framework	1077
+Walls: the cheeks	1080 Floor	1081
+Tongue	1084 Salivary glands	1091 Roof—palate      1095
+Conceptual Overview  •  General Description	8
+
+
+
+
+
+Oral fissure and lips	1103 Oropharyngeal isthmus      1104 Teeth and gingivae      1104
+
+Surface anatomy	1110
+Head and neck surface anatomy	1110 Anatomical position of the head and major
+landmarks	1110
+Visualizing structures at the CIII/CIV and CVI vertebral levels	1111
+How to outline the anterior and posterior triangles of the neck	1112
+How to locate the cricothyroid ligament	1113
+
+How to find the thyroid gland	1114
+Estimating the position of the middle meningeal artery	1114
+Major features of the face	1115
+The eye and lacrimal apparatus	1116 External ear	1117
+Pulse points	1118
+
+Clinical cases	1119
+
+
+
+
+
+
+
+
+Conceptual overview GENERAL DESCRIPTION
+
+
+The head and neck are anatomically complex areas of the body.
+
+
+Head
+Major compartments
+The head is composed of a series of compartments, which are formed by bone and soft tissues. They are:
+
+cranial cavity, and the apex of each cone is directed pos-teromedially. The walls of the orbits are bone, whereas the base of each conical chamber can be opened and closed by the eyelids.
+The nasal cavities are the upper parts of the respira-tory tract and are between the orbits. They have walls, floors, and ceilings, which are predominantly composed of bone and cartilage. The anterior openings to the nasal
+
+
+
+
+■     the cranial cavity, ■     two ears,
+■     two orbits,
+■     two nasal cavities, and ■     an oral cavity (Fig. 8.1).
+
+cavities are nares (nostrils), and the posterior openings are choanae (posterior nasal apertures).
+Continuous   with   the   nasal   cavities   are   air-filled extensions (paranasal sinuses), which project laterally, superiorly,   and   posteriorly   into   surrounding   bones. The largest, the maxillary sinuses, are inferior to the orbits.
+
+The   cranial   cavity   is   the   largest   compartment           The oral cavity is inferior to the nasal cavities, and and   contains   the   brain   and   associated   membranes       separated from them by the hard and soft palates. The
+
+(meninges).
+Most of  the ear apparatus on each side is contained within one of the bones forming the floor of the cranial cavity. The external parts of the ears extend laterally from these regions.
+The two orbits contain the eyes. They are cone-shaped chambers immediately inferior to the anterior aspect of the
+
+floor of the oral cavity is formed entirely of soft tissues. The anterior opening to the oral cavity is the oral
+fissure (mouth), and the posterior opening is the oropha-ryngeal isthmus. Unlike the nares and choanae, which are continuously open, both the oral fissure and oropha-ryngeal isthmus can be opened and closed by surrounding soft tissues.
+
+
+
+825
+Head and Neck
+
+
+
+
+
+
+Ears	Cranial cavity
+
+
+
+
+
+
+Orbits
+
+
+Nasal cavities and paranasal sinuses
+
+
+Nares
+
+Oral fissure
+
+
+
+Choanae
+
+
+Oropharyngeal isthmus
+
+
+Oral cavity
+
+
+
+
+
+
+
+
+
+Fig. 8.1  Major compartments of the head and neck.
+
+
+
+Other anatomically defined regions
+In addition to the major compartments of the head, two other anatomically defined regions (infratemporal fossa and pterygopalatine fossa) of  the head on each side are areas of transition from one compartment of the head to another (Fig. 8.2). The face and scalp also are anatomically defined  areas  of  the  head  and  are  related  to  external surfaces.
+The infratemporal fossa is an area between the pos-terior aspect (ramus) of the mandible and a flat region of bone (lateral plate of the pterygoid process) just posterior to the upper jaw (maxilla). This fossa, bounded by bone and soft  tissues,  is  a  conduit  for  one  of  the  major  cranial nerves—the mandibular nerve (the mandibular division of the  trigeminal  nerve  [V3]),  which  passes  between  the cranial and oral cavities.
+The pterygopalatine fossa on each side is just poste-rior to the upper jaw. This small fossa communicates with the cranial cavity, the infratemporal fossa, the orbit, the nasal cavity, and the oral cavity. A major structure passing
+
+
+
+Pterygopalatine fossa
+
+Maxillary nerve [V2]
+
+
+
+Lateral plate of pterygoid process
+
+Mandibular nerve [V3]
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Infratemporal fossa
+
+
+Ramus of mandible
+
+through the pterygopalatine fossa is the maxillary nerve 826	(the maxillary division of the trigeminal nerve [V2]).
+
+Fig. 8.2  Areas of transition from one compartment of the head to another.
+Conceptual Overview  •  General Description	8
+
+
+Scalp
+
+
+
+
+
+
+
+Orbicularis oculi
+
+
+
+
+Orbicularis oris
+
+
+Face
+
+
+
+Fig. 8.3  Muscles of the face.
+
+
+
+
+
+
+
+The face is the anterior aspect of the head and contains a unique group of muscles that move the skin relative to underlying bone and control the anterior openings to the orbits and oral cavity (Fig. 8.3).
+The scalp covers the superior, posterior, and lateral regions of the head (Fig. 8.3).
+
+
+Superior nuchal line
+
+
+
+Mastoid process
+
+
+
+
+Neck
+The neck extends from the head above to the shoulders and thorax below (Fig. 8.4). Its superior boundary is along the inferior margins of the mandible and bone features on the posterior aspect of  the skull. The posterior neck is higher than the anterior neck to connect cervical viscera with the posterior openings of the nasal and oral cavities. The inferior boundary of the neck extends from the top
+of the sternum, along the clavicle, and onto the adjacent acromion, a bony projection of the scapula. Posteriorly, the inferior limit of the neck is less well defined, but can be approximated by a line between the acromion and the spinous process of vertebra CVII, which is prominent and easily palpable. The inferior border of the neck encloses the base of the neck.
+
+
+
+
+
+
+Mandible
+
+
+Vertebra CVII
+
+
+
+
+
+
+
+
+Clavicle	Manubrium of sternum	Acromion
+
+
+Fig. 8.4  Boundaries of the neck.
+
+
+
+827
+Head and Neck
+
+
+Compartments	Visceral compartment
+
+The neck has four major compartments (Fig. 8.5), which are enclosed by an outer musculofascial collar:
+
+
+Musculofascial collar
+(investing fascia)	Anterior
+
+
+Vascular compartment
+
+
+■     The vertebral compartment contains the cervical verte-brae and associated postural muscles.
+■     The visceral compartment contains important glands (thyroid, parathyroid, and thymus), and parts of  the respiratory and digestive tracts that pass between the head and thorax.
+■     The  two  vascular  compartments,  one  on  each  side, contain the major blood vessels and the vagus nerve.
+
+
+Larynx and pharynx
+The neck contains two specialized structures associated with the digestive and respiratory tracts—the larynx and pharynx.
+The larynx (Fig. 8.6) is the upper part of  the lower airway and is attached below to the top of the trachea and above, by a flexible membrane, to the hyoid bone, which in turn is attached to the floor of the oral cavity. A number of cartilages form a supportive framework for the larynx, which has a hollow central channel. The dimensions of
+
+
+
+
+
+
+
+
+Posterior
+
+Vertebral compartment
+
+Fig. 8.5  Major compartments of the neck.
+
+
+
+
+Nasal cavities
+
+Airway
+
+
+
+Laryngeal inlet Nasopharynx
+
+Epiglottis
+
+
+Laryngo-pharynx
+
+Pharynx
+
+
+
+
+
+
+Oral cavity
+
+Larynx
+
+Oropharynx
+
+
+Laryngopharynx
+
+Laryngeal inlet
+
+
+
+Vocal cords
+
+
+
+
+Thyroid cartilage
+
+
+Inferior constrictor muscle
+
+
+
+Trachea A
+
+
+Esophagus
+Cricoid cartilage	Esophagus
+
+
+
+
+Trachea
+
+
+B
+828	Fig. 8.6  Specialized structures of the neck. A. Conceptual view. B. Anatomical view.
+Conceptual Overview  •  Functions	8
+
+
+
+this central channel can be adjusted by soft tissue struc-tures associated with the laryngeal wall. The most impor-tant of  these are two lateral vocal folds, which project toward each other from adjacent sides of  the laryngeal cavity. The upper opening of the larynx (laryngeal inlet) is tilted posteriorly, and is continuous with the pharynx.
+The pharynx (Fig. 8.6) is a chamber in the shape of a half-cylinder with walls formed by muscles and fascia. Above, the walls are attached to the base of the skull, and below to the margins of the esophagus. On each side, the walls are attached to the lateral margins of the nasal cavi-ties, the oral cavity, and the larynx. The two nasal cavities, the oral cavity, and the larynx therefore open into the anterior aspect of the pharynx, and the esophagus opens inferiorly.
+The part of the pharynx posterior to the nasal cavities is the nasopharynx. Those parts posterior to the oral cavity and larynx are the oropharynx and laryngophar-ynx, respectively.
+
+
+FUNCTIONS Protection
+The head houses and protects the brain and all the receptor systems associated with the special senses—the nasal cavi-ties associated with smell, the orbits with vision, the ears with hearing and balance, and the oral cavity with taste.
+
+Contains upper parts of respiratory and digestive tracts
+
+The head contains the upper parts of the respiratory and digestive  systems—the  nasal  and  oral  cavities—which
+
+have  structural  features  for  modifying  the  air  or  food passing into each system.
+
+
+Communication
+The head and neck are involved in communication. Sounds produced by the larynx are modified in the pharynx and oral cavity to produce speech. In addition, the muscles of facial expression adjust the contours of the face to relay nonverbal signals.
+
+
+Positioning the head
+The neck supports and positions the head. Importantly, it enables an individual to position sensory systems in the head relative to environmental cues without moving the entire body.
+
+
+Connects the upper and lower respiratory and digestive tracts
+
+The neck contains specialized structures (pharynx and larynx) that connect the upper parts of the digestive and respiratory tracts (nasal and oral cavities) in the head, with the esophagus and trachea, which begin relatively low in the neck and pass into the thorax.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+829
+Head and Neck
+
+
+
+COMPONENT PARTS Skull
+The many bones of the head collectively form the skull (Fig. 8.7A). Most of these bones are interconnected by sutures, which are immovable fibrous joints (Fig. 8.7B).
+In the fetus and newborn, large membranous and unos-sified gaps (fontanelles) between the bones of the skull, particularly between the large flat bones that cover the top of the cranial cavity (Fig. 8.7C), allow:
+
+Most of the fontanelles close during the first year of life. Full ossification of  the thin connective tissue ligaments separating the bones at the suture lines begins in the late twenties, and is normally completed in the fifth decade of life.
+There are only three pairs of synovial joints on each side in the head. The largest are the temporomandibular joints between the lower jaw (mandible) and the temporal bone. The other two synovial joints are between the three tiny bones in the middle ear, the malleus, incus, and stapes.
+
+
+■     the head to deform during its passage through the birth canal, and
+■     postnatal growth.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+A
+
+
+830	Fig. 8.7  Skull. A. Bones.
+Conceptual Overview  •  Component Parts	8
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Coronal suture	Sagittal suture
+
+
+
+Coronal suture
+
+
+Sagittal suture
+
+
+
+
+Lambdoid suture
+
+
+
+
+
+
+Anterior fontanelle
+
+
+
+
+
+Posterior fontanelle
+
+
+B	C
+
+Fig. 8.7, cont’d  Skull. B. Sutures. C. Fontanelles and lambdoid suture.
+
+
+
+
+
+
+
+
+
+
+
+
+831
+Head and Neck
+
+
+
+
+Cervical vertebrae
+The seven cervical vertebrae form the bony framework of the neck.
+
+■     transverse processes that contain a foramen (foramen transversarium).
+
+Together the foramina transversaria form a longitudinal
+
+Cervical vertebrae (Fig. 8.8A) are characterized by:
+
+■     small bodies,
+■     bifid spinous processes, and
+
+
+passage on each side of the cervical vertebral column for blood vessels (vertebral artery and veins) passing between the base of the neck and the cranial cavity.
+
+
+Arch	Spinous process
+Superior articular facet
+
+
+
+
+
+
+
+Body
+
+A	Anterior tubercle
+
+Anterior arch
+
+Foramen transversarium Posterior tubercle
+
+Transverse process
+
+
+
+
+Dens Lateral mass	Articular facet
+for dens
+
+
+
+B	Posterior arch	C	Body
+
+
+
+Superior articular surface (for occipital condyle)
+
+
+Articular facet for dens
+
+Superior longitudinal band of cruciform ligament
+Tectorial membrane (upper part of posterior longitudinal ligament)
+Occipital bone
+
+Apical ligament of dens
+
+
+Alar ligaments
+Foramen magnum
+
+
+
+Atlas (CI)
+
+
+
+Occipital condyle D	Axis (CII)
+
+
+Transverse ligament of atlas
+
+Inferior longitudinal band
+of cruciform ligament	E
+
+
+
+Posterior longitudinal ligament
+
+
+Fig. 8.8  Cervical vertebrae. A. Typical features. B. Atlas—vertebra CI (superior view). C. Axis—vertebra CII (anterior view). D. Atlas and axis 832	(anterolateral view). E. Atlanto-occipital joint (posterior view).
+Conceptual Overview  •  Component Parts	8
+
+
+
+The typical transverse process of a cervical vertebra also has anterior and posterior tubercles for muscle attach-ment. The anterior tubercles are derived from the same embryological elements that give rise to ribs in the thoracic region. Occasionally, cervical ribs develop from these ele-ments, particularly in association with the lower cervical
+
+■     The body of the hyoid bone is anterior and forms the base of the U.
+■     The two arms of the U (greater horns) project poste-riorly from the lateral ends of the body.
+
+The hyoid bone does not articulate directly with any
+
+
+
+vertebrae.
+The  upper  two  cervical  vertebrae  (CI  and  CII)  are modified  for  moving  the  head  (Fig.  8.8B–E;  see  also Chapter 2).
+
+Hyoid bone
+
+other skeletal elements in the head and neck.
+The hyoid bone is a highly movable and strong bony anchor for a number of muscles and soft tissue structures in the head and neck. Significantly, it is at the interface between three dynamic compartments:
+
+
+
+The hyoid bone is a small U-shaped bone (Fig. 8.9A) ori-ented in the horizontal plane just superior to the larynx, where it can be palpated and moved from side to side.
+
+
+■     Superiorly, it is attached to the floor of the oral cavity. ■     Inferiorly, it is attached to the larynx.
+■     Posteriorly, it is attached to the pharynx (Fig. 8.9B).
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Greater horn
+
+Stylohyoid ligament
+
+Lesser horn
+Middle pharyngeal constrictor muscle
+Epiglottis
+
+
+
+
+
+Body of hyoid bone
+
+A
+
+Floor of mouth (mylohyoid muscle)
+
+Thyrohyoid membrane
+
+
+Inferior pharyngeal constrictor muscle
+
+
+
+
+
+
+
+B
+
+
+Fig. 8.9  Hyoid. A. Bone. B. Attachments.	833
+Head and Neck
+
+
+
+Soft palate	■
+
+muscles  of   mastication  (move  the  jaw—temporo-mandibular joint),
+
+The soft palate is a soft tissue flap-like structure “hinged” to the back of  the hard palate (Fig. 8.10A) with a free posterior  margin.  It  can  be  elevated  and  depressed  by muscles (Fig. 8.10B).
+The soft palate and associated structures can be clearly
+
+■     muscles  of  the  soft  palate  (elevate  and  depress  the palate), and
+■     muscles of the tongue (move and change the contour of the tongue).
+
+
+
+seen through an open mouth.
+
+Muscles
+
+
+In the neck
+In the neck, major muscle groups include:
+
+
+
+The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation.
+
+In the head
+The muscle groups in the head include:
+
+
+■     muscles  of  the  pharynx  (constrict  and  elevate  the pharynx),
+■     muscles of the larynx (adjust the dimensions of the air pathway),
+■     strap muscles (position the larynx and hyoid bone in the neck),
+
+
+
+■     the extra-ocular muscles (move the eyeball and open the upper eyelid),
+■     muscles of the middle ear (adjust the movement of the middle ear bones),
+■     muscles of facial expression (move the face),
+
+■     muscles of the outer cervical collar (move the head and upper limb), and
+■     postural muscles in the muscular compartment of the neck (position the neck and head).
+
+
+
+
+
+
+Oral cavity	Tensor veli palatini muscle
+
+Soft palate	Choanae
+
+Levator veli palatini muscle
+
+
+Nasopharynx
+
+
+
+
+Oropharynx
+
+Pharynx
+
+Pharynx
+
+Palatine tonsil
+
+Palatopharyngeus Laryngopharynx	muscle
+
+
+
+Oropharyngeal isthmus
+A
+
+
+Tongue
+
+Hyoid bone
+
+Palatoglossus muscle
+
+
+
+
+B
+
+834	Fig. 8.10  Soft palate. A. Position. B. Muscles.
+Conceptual Overview  •  Relationship to Other Regions	8
+
+
+
+RELATIONSHIP TO OTHER REGIONS Thorax
+The superior thoracic aperture (thoracic inlet) opens directly into the base of the neck (Fig. 8.11). Structures passing between the head and thorax pass up and down
+
+
+Upper limbs
+There is an axillary inlet (gateway to the upper limb) on each side of the superior thoracic aperture at the base of the neck (Fig. 8.11):
+
+through the superior thoracic aperture and the visceral compartment of  the neck. At the base of  the neck, the trachea is immediately anterior to the esophagus, which is directly anterior to the vertebral column. There are major veins,  arteries,  and  nerves  anterior  and  lateral  to  the trachea.
+
+■     Structures such as blood vessels pass over rib I when passing between the axillary inlet and thorax.
+■     Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb.
+
+
+
+
+
+
+
+
+
+Superior thoracic aperture
+
+Brachial plexus
+
+Axillary inlet
+
+
+Esophagus
+Trachea
+
+Scapula
+
+
+
+
+Rib I
+
+
+Subclavian artery and vein	Clavicle
+
+
+
+
+
+
+
+Fig. 8.11  Superior thoracic aperture and axillary inlets.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+835
+Head and Neck
+
+
+
+KEY FEATURES
+Vertebral levels CIII/IV and CV/VI
+In  the  neck,  the  two  important  vertebral  levels  (Fig. 8.12) are:
+
+■     between CV and CVI, which marks the lower limit of the pharynx and larynx, and the superior limit of the trachea and esophagus—the indentation between the cricoid cartilage of the larynx and the first tracheal ring can be palpated.
+
+
+
+■     between CIII and CIV, at approximately the superior border of the thyroid cartilage of the larynx (which can be palpated) and where the major artery on each side of the neck (the common carotid artery) bifurcates into internal and external carotid arteries; and
+
+
+The internal carotid artery has no branches in the neck and ascends into the skull to supply much of the brain. It also supplies the eye and orbit. Other regions of the head and neck are supplied by branches of the external carotid artery.
+
+
+
+
+
+
+
+
+
+
+
+External carotid artery
+
+Internal carotid artery
+
+
+
+
+Pharynx
+
+
+CIII–CIV level
+
+Thyroid cartilage
+
+Cricoid cartilage
+
+
+
+Trachea
+
+Esophagus
+
+CV–CVI level
+
+Common carotid artery
+
+
+
+Fig. 8.12  Important vertebral levels—CIII/CIV and CV/CVI.
+
+
+
+
+
+
+
+
+
+
+
+
+836
+Conceptual Overview  •  Key Features	8
+
+
+
+
+Airway in the neck
+The larynx (Fig. 8.13) and the trachea are anterior to the digestive tract in the neck, and can be accessed directly when upper parts of the system are blocked. A cricothy-rotomy makes use of the easiest route of access through the cricothyroid ligament (cricovocal membrane, crico-thyroid  membrane)  between  the  cricoid  and  thyroid
+
+cartilages of the larynx. The ligament can be palpated in the midline, and usually there are only small blood vessels, connective tissue, and skin (though occasionally, a small lobe of the thyroid gland—pyramidal lobe) overlying it. At a lower level, the airway can be accessed surgically through the anterior wall of the trachea by tracheostomy. This route of entry is complicated because large veins and part of the thyroid gland overlie this region.
+
+
+
+
+
+
+
+
+
+
+
+
+Hyoid
+
+
+
+
+Superior thyroid artery
+
+
+
+Median cricothyroid ligament
+
+Thyroid cartilage
+
+Larynx
+
+Cricoid cartilage
+
+
+
+Omohyoid
+Thyroid gland
+
+Sternohyoid	Inferior thyroid veins
+
+
+
+
+
+
+
+
+
+
+Fig. 8.13  Larynx and associated structures in the neck.
+
+
+
+
+
+
+
+
+
+
+
+837
+Head and Neck
+
+
+
+
+Cranial nerves
+There are twelve pairs of cranial nerves and their defining feature is that they exit the cranial cavity through foramina or fissures.
+All cranial nerves innervate structures in the head or neck. In addition, the vagus nerve [X] descends through the neck and into the thorax and abdomen where it inner-vates viscera.
+Parasympathetic fibers in the head are carried out of the brain as part of four cranial nerves—the oculomotor nerve
+
+[III], the facial nerve [VII], the glossopharyngeal nerve [IX], and the vagus nerve [X] (Fig. 8.14). Parasympathetic fibers in the oculomotor nerve [III], the facial nerve [VII], and the glossopharyngeal nerve [IX] destined for target tissues in the head leave these nerves, and are distributed with branches of the trigeminal nerve [V].
+The vagus nerve [X] leaves the head and neck to deliver parasympathetic  fibers  to  the  thoracic  and  abdominal viscera.
+
+
+
+
+
+
+
+Ciliary ganglion	Ophthalmic nerve [V1]
+
+Oculomotor nerve [III]
+Trigeminal nerve [V]	Facial nerve [VII] Mandibular nerve [V3]
+
+
+Vagus nerve [X]
+
+
+
+
+
+
+
+Pterygopalatine ganglion
+
+
+
+Otic ganglion
+
+Maxillary nerve [V2]
+
+
+
+
+
+Glossopharyngeal nerve [IX]
+
+
+
+Submandibular ganglion
+
+
+Preganglionic parasympathetic fibers
+
+Postganglionic parasympathetic fibers
+
+
+Fig. 8.14  Cranial nerves and parasympathetic innervation.
+
+
+
+
+
+
+
+
+838
+Conceptual Overview  •  Key Features	8
+
+
+
+
+Cervical nerves
+There are eight cervical nerves (C1 to C8):
+
+thoracic wall, and skin on the inferior parts of the head (Fig. 8.15B).
+The anterior rami of  C5 to C8, together with a large
+
+
+
+
+■     C1 to C7 emerge from the vertebral canal above their respective vertebrae.
+■     C8 emerges between vertebrae CVII and TI (Fig. 8.15A).
+
+The anterior rami of C1 to C4 form the cervical plexus.
+
+component of the anterior ramus of T1, form the brachial plexus, which innervates the upper limb.
+
+
+Functional separation of the digestive and respiratory passages
+
+
+
+The major branches from this plexus supply the strap muscles, the diaphragm (phrenic nerve), skin on the ante-rior and lateral parts of the neck, skin on the upper anterior
+
+The pharynx is a common chamber for the digestive and respiratory tracts. Consequently, breathing can take place through  the  mouth  as  well  as  through  the  nose,  and
+
+
+
+
+
+
+
+
+
+
+
+
+Cutaneous nerves
+
+Cervical plexus (C1 to C4)
+
+
+
+Ansa cervicalis to strap muscles
+
+
+Brachial plexus (C5 to T1)
+
+
+Phrenic nerve
+
+
+
+
+
+A
+Trigeminal nerve [V]
+
+
+Ophthalmic nerve [V1] C2
+
+
+
+External occipital protuberance
+C2
+
+Posterior rami (C2 to C4)	C3
+
+Acromion	C3
+
+
+Maxillary nerve [V2]
+
+Mandibular nerve [V3]
+
+
+Anterior rami (C2 to C4)
+
+
+
+C4
+B	C4
+
+
+Clavicle
+
+
+Fig. 8.15  Cervical nerves. A. Structure. B. Dermatomes.	839
+Head and Neck
+
+
+
+material from the oral cavity can potentially enter either the esophagus or the larynx. Importantly:
+
+Normally,  the  soft  palate,  epiglottis,  and  soft  tissue structures within the larynx act as valves to prevent food
+
+
+
+
+■     The lower airway can be accessed through the oral cavity by intubation.
+■     The digestive tract (esophagus) can be accessed through the nasal cavity by feeding tubes.
+
+and liquid from entering lower parts of  the respiratory tract (Fig. 8.16A).
+During normal breathing, the airway is open and air passes freely through the nasal cavities (or oral cavity), pharynx, larynx, and trachea (Fig. 8.16A). The lumen of
+
+
+
+
+Choanae
+Cranial cavity
+
+
+
+
+Ears Orbits
+
+
+
+
+Nasal cavities
+
+
+Oral cavity
+
+
+
+Epiglottis (opens and closes laryngeal inlet)
+
+Vocal folds (together with other soft tissue
+structures open and close cavity of larynx)
+
+
+
+Trachea
+
+
+Manubrium of sternum
+
+
+Nasopharynx
+
+Soft palate
+(opens and closes
+oropharyngeal isthmus)		Pharynx Oropharynx
+
+Oropharyngeal isthmus
+Laryngopharynx
+Laryngeal inlet
+Larynx
+
+CVI vertebral level
+
+
+Esophagus
+
+Vertebra TI
+
+
+Rib I
+
+
+Superior thoracic aperture (thoracic inlet)
+
+
+
+Clavicle
+Scapula
+
+Axillary inlet
+
+
+
+A
+
+840	Fig. 8.16  Larynx, soft palate, epiglottis, and oropharyngeal isthmus. A. Overall design.
+Conceptual Overview  •  Key Features	8
+
+
+
+Soft palate in neutral position
+
+Oropharyngeal isthmus closed
+
+
+
+
+
+
+
+
+
+
+
+Laryngeal inlet and laryngeal cavity open
+
+
+Back of tongue elevated,
+palate depressed
+
+B		C Opening between nasal and
+oral parts of pharynx closed by soft palate
+
+
+Nasal cavity	Soft palate
+
+
+
+
+
+Oropharyngeal isthmus open
+
+
+Milk pathway
+
+
+Laryngeal inlet
+
+
+
+
+
+
+Larynx and hyoid pulled up and forward
+resulting in opening the esophagus
+
+D
+
+
+Epiglottis closed over laryngeal inlet
+
+
+
+Trachea	Esophagus
+
+E
+
+
+
+Fig. 8.16, cont’d  B. Normal breathing. C. Breathing with food or liquid in the oral cavity. D. Swallowing. E. In a newborn child.
+
+
+
+
+the  esophagus  is  normally  closed  because,  unlike  the airway, it has no skeletal support structures to hold it open. When the oral cavity is full of liquid or food, the soft palate is swung down (depressed) to close the oropharyn-geal isthmus, thereby allowing manipulation of food and
+fluid in the oral cavity while breathing (Fig. 8.16C).
+
+When  swallowing,  the  soft  palate  and  parts  of  the larynx act as valves to ensure proper movement of food from the oral cavity into the esophagus (Fig. 8.16D).
+The  soft  palate  elevates  to  open  the  oropharyngeal isthmus while at the same time sealing off the nasal part
+of the pharynx from the oral part. This prevents food and	841
+Head and Neck
+
+
+
+fluid from moving upward into the nasopharynx and nasal cavities.
+The epiglottis of  the larynx closes the laryngeal inlet and much of  the laryngeal cavity becomes occluded by opposition of the vocal folds and soft tissue folds superior to them. In addition, the larynx is pulled up and forward to facilitate the moving of food and fluid over and around the closed larynx and into the esophagus.
+In newborns, the larynx is high in the neck and the epiglottis is above the level of the soft palate (Fig. 8.16E). Babies can therefore suckle and breathe at the same time. Liquid flows around the larynx without any danger of entering the airway. During the second year of  life, the
+
+The boundaries of each anterior triangle are:
+
+■     the median vertical line of the neck,
+■     the inferior margin of the mandible, and
+■     the anterior margin of the sternocleidomastoid muscle.
+
+The posterior triangle is bounded by:
+
+■     the middle one-third of the clavicle,
+■     the anterior margin of the trapezius, and
+■     the posterior margin of the sternocleidomastoid.
+
+Major structures that pass between the head and thorax
+
+
+
+larynx descends into the low cervical position characteris-tic of adults.
+
+Triangles of the neck
+The two muscles (trapezius and sternocleidomastoid) that form part of the outer cervical collar divide the neck into anterior and posterior triangles on each side (Fig. 8.17).
+
+can be accessed through the anterior triangle.
+The posterior triangle in part lies over the axillary inlet, and is associated with structures (nerves and vessels) that pass into and out of the upper limb.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Anterior midline of neck
+
+Axillary inlet
+
+
+
+
+
+
+
+
+
+Superior thoracic aperture
+
+Anterior triangle
+
+Sternocleidomastoid
+
+Trapezius
+
+Anterior triangle
+Posterior triangle
+
+
+
+
+
+
+Clavicle
+
+
+Sternocleidomastoid
+
+Trapezius
+
+
+Clavicle
+Posterior triangle
+
+
+
+Fig. 8.17  Anterior and posterior triangles of neck.
+
+
+
+
+
+842
+Regional Anatomy  •  Skull	8
+
+
+Regional anatomy SKULL
+
+
+The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile, and form the cranium.
+The cranium can be subdivided into:
+
+The bones forming the base of the cranium are mainly parts of the sphenoid, temporal, and occipital bones.
+The bones forming the facial skeleton are the paired nasal bones, palatine bones, lacrimal bones, zygomatic bones,  maxillae  and  inferior  nasal  conchae  and  the
+
+
+
+
+■     an upper domed part (the calvaria), which covers the cranial cavity containing the brain,
+■     a base that consists of the floor of the cranial cavity, and
+
+unpaired vomer.
+The mandible is not part of the cranium nor part of the facial skeleton.
+
+
+
+■     a	lower	anterior	part—the	facial	skeleton (viscerocranium).
+
+
+Anterior view
+The  anterior  view  of  the  skull  includes  the  forehead
+
+
+
+The bones forming the calvaria are mainly the paired temporal and parietal bones, and parts of  the unpaired frontal, sphenoid, and occipital bones.
+
+superiorly, and, inferiorly, the orbits, the nasal region, the part of the face between the orbit and the upper jaw, the upper jaw, and the lower jaw (Fig. 8.18).
+
+
+
+
+
+
+Superciliary arch
+
+Frontal bone
+
+Supra-orbital notch (foramen)
+
+
+Glabella
+
+
+Nasion
+
+
+
+Piriform aperture
+
+Inferior nasal concha
+
+
+
+
+Zygomatic process (of maxilla)
+
+
+Ramus of mandible
+
+Maxilla
+
+Angle of mandible
+
+Body of mandible
+
+
+
+Zygomatic process (of frontal bone)
+Nasal bone
+
+
+Frontal process (of maxilla) Zygomatic bone
+Infra-orbital foramen Nasal crest
+
+
+Anterior nasal spine Alveolar process
+
+Oblique line
+
+
+Alveolar part of mandible
+
+
+Mandible
+
+Mental foramen
+
+
+Mental protuberance	Mental tubercle
+Fig. 8.18  Anterior view of the skull.	843
+Head and Neck
+
+
+
+
+Frontal bone
+The forehead consists of  the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.18). Just superior to the rim of the orbit on each side are the raised superciliary arches. These are more pronounced in men than in women. Between these arches is a small
+depression (the glabella).
+Clearly visible in the medial part of the superior rim of each orbit is the supra-orbital foramen (supra-orbital notch; Table 8.1).
+Medially, the frontal bone projects inferiorly forming a part of the medial rim of the orbit.
+Laterally, the zygomatic process of the frontal bone projects inferiorly forming the upper lateral rim of  the
+
+orbit. This process articulates with the frontal process of the zygomatic bone.
+
+Zygomatic and nasal bones
+The lower lateral rim of the orbit, as well as the lateral part of the inferior rim of the orbit is formed by the zygomatic bone (the cheekbone).
+Superiorly, in the nasal region the paired nasal bones articulate with each other in the midline, and with the frontal bone superiorly. The center of  the frontonasal suture formed by the articulation of the nasal bones and the frontal bone is the nasion.
+Laterally, each nasal bone articulates with the frontal process of each maxilla.
+Inferiorly, the piriform aperture is the large opening in the nasal region and the anterior opening of the nasal
+
+
+Table 8.1
+
+
+Foramen
+
+
+External foramina of the skull
+
+Structures passing through foramen
+
+cavity. It is bounded superiorly by the nasal bones and laterally and inferiorly by each maxilla.
+Visible  through  the  piriform  aperture  are  the  fused nasal crests, forming the lower part of the bony nasal
+
+
+
+ANTERIOR VIEW
+Supra-orbital foramen
+Infra-orbital foramen Mental foramen
+LATERAL VIEW Zygomaticofacial foramen
+SUPERIOR VIEW
+Parietal foramen
+
+
+Supra-orbital nerve and vessels Infra-orbital nerve and vessels Mental nerve and vessels
+
+Zygomaticofacial nerve
+
+Emissary veins
+
+septum and ending anteriorly as the anterior  nasal spine, and the paired inferior nasal conchae.
+
+Maxillae
+The part of the face between the orbit and the upper teeth and each upper jaw is formed by the paired maxillae.
+Superiorly, each maxilla contributes to the inferior and medial rims of the orbit.
+
+INFERIOR VIEW	Laterally,  the  zygomatic  process  of  each  maxilla
+
+Incisive foramen
+
+Greater palatine foramen Lesser palatine foramen Pterygoid canal
+
+Foramen ovale
+
+Foramen spinosum Foramen lacerum Carotid canal
+
+Foramen magnum
+
+
+
+
+Condylar canal Hypoglossal canal Jugular foramen
+
+
+
+844	Stylomastoid foramen
+
+
+Nasopalatine nerve; sphenopalatine vessels
+Greater palatine nerve and vessels Lesser palatine nerves and vessels
+Nerve of pterygoid canal and vessels
+Mandibular nerve [V3]; lesser petrosal nerve
+Middle meningeal artery Filled with cartilage
+Internal carotid artery and nerve plexus
+Continuation of brain and spinal cord; vertebral arteries and nerve plexuses; anterior spinal artery; posterior spinal arteries; roots of accessory nerve [XI]; meninges
+Emissary veins
+Hypoglossal nerve [XII] and vessels
+Internal jugular vein; inferior petrosal sinus; glossopharyngeal nerve [IX]; vagus nerve [X]; accessory nerve [XI]
+Facial nerve [VII]
+
+articulates  with  the  zygomatic  bone  and  medially,  the frontal  process  of   each  maxilla  articulates  with  the frontal bone.
+Inferiorly, the part of each maxilla, lateral to the opening of the nasal cavity, is the body of the maxilla.
+On the anterior surface of the body of the maxilla, just below the inferior rim of  the orbit, is the infra-orbital foramen (Table 8.1).
+Inferiorly, each maxilla ends as the alveolar process, which contains the teeth and forms the upper jaw.
+
+Mandible
+The lower jaw (mandible) is the most inferior structure in the anterior view of the skull. It consists of the body of the mandible anteriorly and the ramus of the man-dible posteriorly. These meet posteriorly at the angle of the mandible. All these parts of the mandible are visible, to some extent, in the anterior view.
+The body of  the mandible is arbitrarily divided into two parts:
+
+■     The lower part is the base of the mandible.
+■     The upper part is the alveolar part of the mandible.
+Regional Anatomy  •  Skull	8
+
+
+
+The alveolar part of  the mandible contains the teeth and is resorbed when the teeth are removed. The base of the mandible has a midline swelling (the mental protu-berance) on its anterior surface where the two sides of the mandible come together. Just lateral to the mental protu-berance,  on  either  side,  are  slightly  more  pronounced bumps (mental tubercles).
+Laterally,  a  mental  foramen  (Table  8.1)  is  visible halfway between the upper border of the alveolar part of the mandible and the lower border of  the base of  the
+
+mandible. Continuing past this foramen is a ridge (the oblique line) passing from the front of the ramus onto the body of the mandible. The oblique line is a point of attach-ment for muscles that depress the lower lip.
+
+Lateral view
+The lateral view of  the skull consists of  the lateral wall of  the cranium, which includes lateral portions of  the calvaria and the facial skeleton, and half of the lower jaw (Fig. 8.19):
+
+
+
+
+
+
+Sphenoparietal suture
+
+Coronal suture
+
+Sphenosquamous suture
+
+Squamous suture
+
+Squamous part (of temporal bone)
+
+
+Parietal bone
+Pterion
+
+
+
+Frontal bone
+
+
+Greater wing (of sphenoid bone)
+
+Zygomaticotemporal foramen
+(on deep surface of zygomatic bone)
+
+Lacrimal bone
+
+Nasal bone
+
+Zygomaticofacial foramen
+
+Zygomatic bone
+
+
+Maxilla
+
+
+Parietomastoid suture
+
+
+
+
+
+
+Lambdoid suture
+
+
+Asterion
+
+
+Occipital bone
+
+
+Occipitomastoid suture
+Mastoid part of temporal bone
+
+
+Mastoid process
+
+
+Alveolar part (of mandible)
+
+Mental foramen
+
+
+
+Body of mandible
+
+Tympanic part (of temporal bone)
+
+Styloid process
+
+Condylar process
+
+Angle
+
+Ramus of mandible
+Zygomatic process (of temporal bone)
+
+
+Temporal process (of zygomatic bone)	Coronoid process
+
+Fig. 8.19  Lateral view of the skull.	845
+Head and Neck
+
+
+
+■     Bones forming the lateral portion of the calvaria include the frontal, parietal, occipital, sphenoid, and temporal bones.
+■     Bones forming the visible part of  the facial skeleton include the nasal, maxilla, and zygomatic bones.
+■     The mandible forms the visible part of the lower jaw.
+
+opening leading to the external acoustic meatus (ear canal).
+■     The petromastoid part, which is usually separated into a petrous part and a mastoid part for descriptive purposes.
+
+The mastoid part is the most posterior part of the tem-
+
+
+
+
+Lateral portion of the calvaria
+The lateral portion of the calvaria begins anteriorly with the frontal bone. In upper regions, the frontal bone articu-lates with the parietal bone at the coronal suture. The parietal bone then articulates with the occipital bone at the lambdoid suture.
+In lower parts of the lateral portion of the calvaria, the frontal bone articulates with the greater wing of  the sphenoid bone (Fig. 8.19), which then articulates with the parietal bone at the sphenoparietal suture, and with the anterior edge of  the temporal bone at the spheno-squamous suture.
+The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity is the pterion. The clinical consequences of a skull fracture in this area can be very serious. The bone in this area is particularly thin and overlies  the  anterior  division  of  the  middle  meningeal artery, which can be torn by a skull fracture in this area,
+
+poral bone, and is the only part of the petromastoid part of the temporal bone seen on a lateral view of the skull. It is continuous with the squamous part of the temporal bone anteriorly, and articulates with the parietal bone superiorly at the parietomastoid suture, and with the occipital bone posteriorly at the occipitomastoid suture. These two sutures are continuous with each other, and the parieto-mastoid suture is continuous with the squamous suture.
+Inferiorly,  a  large  bony  prominence  (the  mastoid process) projects from the inferior border of the mastoid part of the temporal bone. This is a point of attachment for several muscles.
+Medial to the mastoid process, the styloid process pro-jects from the lower border of the temporal bone.
+
+Visible part of the facial skeleton
+The bones of the viscerocranium visible in a lateral view of  the skull include the nasal, maxilla, and zygomatic bones (Fig. 8.19) as follows:
+
+
+
+resulting in an extradural hematoma.
+The final articulation across the lower part of the lateral portion of the calvaria is between the temporal bone and the occipital bone at the occipitomastoid suture.
+
+Temporal bone
+A major contributor to the lower portion of the lateral wall of  the cranium is the temporal bone (Fig. 8.19), which consists of several parts:
+
+
+■     A nasal bone anteriorly.
+■     The maxilla with its alveolar process containing teeth forming the upper jaw; anteriorly, it articulates with the nasal bone; superiorly, it contributes to the formation of the inferior and medial borders of the orbit; medially, its frontal process articulates with the frontal bone; laterally,  its  zygomatic  process  articulates  with  the zygomatic bone.
+■     The zygomatic bone, an irregularly shaped bone with a
+
+
+
+■     The squamous part has the appearance of  a large flat plate, forms the anterior and superior parts of the temporal bone, contributes to the lateral wall of  the cranium, and articulates anteriorly with the greater wing of  the sphenoid bone at the sphenosquamous suture, and with the parietal bone superiorly at the squamous suture.
+■     The zygomatic process is an anterior bony projection from the lower surface of  the squamous part of  the temporal bone that initially projects laterally and then curves anteriorly to articulate with the temporal process of the zygomatic bone to form the zygomatic arch.
+
+rounded lateral surface that forms the prominence of the cheek, is a visual centerpiece in this view— medially, it assists in the formation of the inferior rim of the orbit through its articulation with the zygomatic process of the maxilla; superiorly, its frontal process articulates with the zygomatic process of the frontal bone assisting in the formation of the lateral rim of the orbit; laterally, seen prominently in this view of the skull, the horizontal temporal process of the zygomatic bone projects back-ward to articulate with the zygomatic process of  the temporal bone and so form the zygomatic arch.
+
+■     Immediately below the origin of the zygomatic process	Usually   a   small   foramen   (the   zygomaticofacial
+
+from the squamous part of  the temporal bone is the tympanic part of the temporal bone, and clearly visible
+846	on the surface of  this part is the external acoustic
+
+foramen; Table 8.1) is visible on the lateral surface of the zygomatic  bone.  A  zygomaticotemporal  foramen  is present on the medial deep surface of the bone.
+Regional Anatomy  •  Skull	8
+
+
+
+Mandible
+The final bony structure visible in a lateral view of the skull is the mandible. Inferiorly in the anterior part of this view, it consists of the anterior body of the mandible, a posterior ramus of  the mandible, and the angle of  the mandible where the inferior margin of the mandible meets the pos-terior margin of the ramus (Fig. 8.19).
+The teeth are in the alveolar part of  the body of  the mandible and the mental protuberance is visible in this view.
+The mental foramen is on the lateral surface of the body, and on the superior part of the ramus condylar and coro-noid processes extend upward.
+The condylar process is involved in articulation of the mandible with the temporal bone, and the coronoid process is the point of attachment for the temporalis muscle.
+
+Posterior view
+The occipital, parietal, and temporal bones are seen in the posterior view of the skull.
+
+Occipital bone
+Centrally the flat or squamous part of  the occipital bone is the main structure in this view of the skull (Fig. 8.20). It articulates superiorly with the paired parietal bones  at  the  lambdoid  suture  and  laterally  with  each temporal bone at the occipitomastoid sutures. Along the lambdoid suture small islands of bone (sutural bones or wormian bones) may be observed.
+Several  bony  landmarks  are  visible  on  the  occipital bone. There is a midline projection (the external occipital protuberance) with curved lines extending laterally from
+
+
+Sagittal suture
+
+
+Sutural bone
+
+
+
+
+
+
+
+
+Parietal bone
+
+
+
+
+
+Lambdoid suture
+
+
+External occipital protuberance
+
+Parietal bone
+
+
+
+
+
+Squamous part of occipital bone
+
+
+Occipitomastoid suture
+
+
+
+Mastoid notch
+
+
+
+
+Mastoid process
+
+Inferior nuchal line
+
+External occipital crest
+
+
+
+
+Fig. 8.20  Posterior view of the skull.
+
+
+Superior nuchal line
+
+
+Inion
+
+
+
+
+847
+Head and Neck
+
+
+
+it (superior nuchal lines). The most prominent point of the external occipital protuberance is the inion. About 1 inch (2.5 cm) below the superior nuchal lines two addi-tional lines (the inferior nuchal lines) curve laterally. Extending downward from the external occipital protuber-ance is the external occipital crest.
+
+■     The two parietal bones articulate with each other in the midline at the sagittal suture.
+■     The parietal bones articulate with the unpaired occipital bone at the lambdoid suture.
+
+The junction of the sagittal and coronal sutures is the
+
+
+
+
+Temporal bones
+Laterally, the temporal bones are visible in the posterior view of  the skull, with the mastoid processes being the prominent feature (Fig. 8.20). On the inferomedial border of each mastoid process is a notch (the mastoid notch), which is a point of attachment for the posterior belly of the digastric muscle.
+
+Superior view
+The frontal bone, parietal bones, and occipital bone are seen in a superior view of the skull (Fig. 8.21). These bones make up the superior part of  the calvaria or the calva (skullcap).
+In an anterior to posterior direction:
+
+bregma, and the junction of  the sagittal and lambdoid sutures is the lambda.
+The only foramina visible in this view of the skull may be the paired parietal foramina, posteriorly, one on each parietal bone just lateral to the sagittal suture (Fig. 8.21). The bones making up the calvaria (Fig. 8.22) are unique
+in their structure, consisting of dense internal and external tables of compact bone separated by a layer of spongy bone (the diploë).
+
+Inferior view
+The base of the skull is seen in the inferior view and extends anteriorly from the middle incisor teeth posteriorly to the superior nuchal lines and laterally to the mastoid processes and zygomatic arches (Fig. 8.23).
+For descriptive purposes the base of the skull is often
+
+■     The unpaired frontal bone articulates with the paired	divided into: parietal bones at the coronal suture.
+
+
+
+
+
+Frontal bone
+
+
+
+
+Coronal suture	Bregma
+
+
+
+
+
+Sagittal suture Parietal bone
+
+
+
+
+Parietal foramen
+
+
+Lambdoid suture
+
+
+Occipital bone	Lambda 848	Fig. 8.21  Superior view of the skull.
+Regional Anatomy  •  Skull	8
+
+
+Scalp	■     the greater palatine foramina near the posterolateral border of the hard palate on each side, which lead to greater palatine canals;
+■     just  posterior  to  the  greater  palatine  foramina,  the lesser palatine foramina in the pyramidal process of each palatine bone, which lead to lesser palatine canals;
+■     a  midline  pointed  projection  (the  posterior  nasal spine) in the free posterior border of the hard palate.
+
+Middle part
+Pericranium	External table	Diploë	The middle part of the base of the skull is complex:
+
+
+Dura	Internal table
+
+Fig. 8.22  Calvaria.
+
+
+■     Forming the anterior half are the vomer and sphenoid bones.
+■     Forming the posterior half are the occipital and paired temporal bones.
+
+
+
+
+■     an  anterior  part,  which  includes  the  teeth  and  the hard palate,
+■     a   middle   part,   which   extends   from   behind   the hard  palate  to  the  anterior  margin  of  the  foramen magnum, and
+■     a  posterior  part,  which  extends  from  the  anterior edge of  the foramen magnum to the superior nuchal lines.
+
+Anterior half Vomer
+Anteriorly, the small vomer is in the midline, resting on the sphenoid bone (Fig. 8.23). It contributes to the formation of the bony nasal septum separating the two choanae.
+
+Sphenoid
+Most of the anterior part of the middle part of the base of the skull consists of the sphenoid bone.
+
+
+
+
+Anterior part
+The main features of the anterior part of the base of the skull are the teeth and the hard palate.
+The teeth project from the alveolar processes of the two maxillae. These processes are together arranged in a U-shaped alveolar arch that borders the hard palate on three sides (Fig. 8.23).
+The hard palate is composed of the palatine proc-esses  of  each  maxilla  anteriorly  and  the  horizontal plates of each palatine bone posteriorly.
+The paired palatine processes of each maxilla meet in the midline at the intermaxillary  suture, the paired maxillae and the paired palatine bones meet at the pala-tomaxillary suture, and the paired horizontal plates of each palatine bone meet in the midline at the interpala-tine suture.
+Several additional features are also visible when the hard palate is examined:
+
+The sphenoid bone is made up of  a centrally placed body, paired greater and lesser wings projecting later-ally from the body, and two downward projecting ptery-goid processes immediately lateral to each choana.
+Three parts of  the sphenoid bone, the body, greater wings, and pterygoid processes, are seen in the inferior view of the skull (Fig. 8.23). The lesser wing of the sphe-noid is not seen in the inferior view.
+
+Body
+The body of the sphenoid is a centrally placed cube of bone containing two large air sinuses separated by a septum.
+It articulates anteriorly with the vomer, ethmoid, and palatine bones, posterolaterally with the temporal bones, and posteriorly with the occipital bone.
+
+Pterygoid processes
+Extending downward from the junction of the body and the greater wings are the pterygoid processes (Fig. 8.23). Each of these processes consists of a narrow medial plate and
+
+■     the incisive fossa in the anterior midline immediately	broader lateral plate separated by the pterygoid fossa. posterior to the teeth, the walls of which contain inci-            Each  medial  plate  of   the  pterygoid  process  ends
+
+sive foramina (the openings of the incisive canals, which are passageways between the hard palate and nasal cavity);
+
+inferiorly  with  a  hook-like  projection,  the  pterygoid hamulus, and divides superiorly to form the small, shallow scaphoid fossa.	849
+Head and Neck
+
+
+Posterior nasal spine	Incisive fossa
+Hard palate (maxilla)
+
+
+Alveolar arch
+
+Posterior nasal aperture (choana)
+
+Pyramidal process of palatine bone
+Hamulus
+
+Vomer Pterygoid fossa
+Greater wing (of sphenoid bone)
+Pterygoid process
+
+Opening of pterygoid canal
+
+Articular tubercle Mandibular fossa Groove for auditory tube
+
+Styloid process Jugular foramen
+
+
+
+Mastoid process
+
+Mastoid notch
+
+Hypoglossal canal
+
+
+Occipital condyle
+
+
+Hard palate (palatine bone)
+
+Greater palatine foramen Lesser palatine foramen
+Body of sphenoid
+
+Medial plate of pterygoid process
+Lateral plate of pterygoid process
+Scaphoid fossa
+
+Foramen lacerum
+
+Foramen ovale
+
+Foramen spinosum
+
+Petrous part of temporal bone
+
+Carotid canal
+
+Stylomastoid foramen
+
+Squamous part of temporal bone
+
+
+
+Basilar part of occipital bone
+
+Pharyngeal tubercle
+
+
+Foramen magnum
+
+External occipital crest	Inferior nuchal line
+
+Superior nuchal line
+
+External occipital protuberance
+
+Fig. 8.23  Inferior view of the skull.
+
+
+
+
+
+Just superior to the scaphoid fossa, at the root of the medial plate of  the pterygoid process is the opening of the pterygoid canal, which passes forward from near the anterior margin of the foramen lacerum.
+
+Greater wing
+Lateral to the lateral plate of the pterygoid process is the 850	greater wing of the sphenoid (Fig. 8.23), which not only
+
+forms a part of  the base of  the skull but also continues laterally to form part of  the lateral wall of  the skull. It articulates laterally and posteriorly with parts of the tem-poral bone.
+Important features visible on the surface of the greater wing in an inferior view of the skull are the foramen ovale and the foramen spinosum on the posterolateral border
+Regional Anatomy  •  Skull	8
+
+
+
+extending outward from the upper end of the lateral plate of the pterygoid process.
+
+Posterior half
+In the posterior half of the middle part of the base of the skull are the occipital bone and the paired temporal bones (Fig. 8.23).
+
+Occipital bone
+The occipital bone, or more specifically its basilar part, is in the midline immediately posterior to the body of  the sphenoid. It extends posteriorly to the foramen magnum and is bounded laterally by the temporal bones.
+Prominent on the basilar part of the occipital bone is the pharyngeal tubercle, a bony protuberance for the attachment of parts of the pharynx to the base of the skull (Fig. 8.23).
+
+Temporal bone
+Immediately lateral to the basilar part of  the occipital bone is the petrous part of the petromastoid part of each temporal bone.
+Wedge-shaped in its appearance, with its apex antero-medial, the petrous part of the temporal bone is between the greater wing of the sphenoid anteriorly and the basilar part of the occipital bone posteriorly. The apex forms one of the boundaries of the foramen lacerum, an irregular opening filled in life with cartilage (Fig. 8.23).
+The other boundaries of the foramen lacerum are the basilar part of the occipital bone medially and the body of the sphenoid anteriorly.
+Posterolateral  from  the  foramen  lacerum  along  the petrous part of  the temporal bone is the large circular opening for the carotid canal.
+Between the petrous part of the temporal bone and the greater wing of the sphenoid is a groove for the cartilagi-nous part of  the pharyngotympanic tube (auditory tube). This groove continues posterolaterally into a bony canal in the petrous part of  the temporal bone for the pharyngotympanic tube.
+Just lateral to the greater wing of the sphenoid is the squamous part of the temporal bone, which participates in the temporomandibular joint. It contains the mandibular fossa, which is a concavity where the head of the mandible articulates with the base of the skull. An important feature of this articulation is the prominent articular tubercle, which is the downward projection of the anterior border of the mandibular fossa (Fig. 8.23).
+
+Posterior part
+The posterior part of the base of the skull extends from the  anterior  edge  of  the  foramen  magnum  posteriorly
+
+to the superior nuchal lines (Fig. 8.23). It consists of parts of  the occipital bone centrally and the temporal bones laterally.
+
+Occipital bone
+The occipital bone is the major bony element of this part of the base of the skull (Fig. 8.23). It has four parts orga-nized around the foramen magnum, which is a prominent feature of this part of the base of the skull and through which the brain and spinal cord are continuous.
+The parts of the occipital bone are the squamous part, which is posterior to the foramen magnum, the lateral parts, which are lateral to the foramen magnum, and the basilar part, which is anterior to the foramen magnum (Fig. 8.23).
+The squamous and lateral parts are components of the posterior part of the base of the skull.
+The most visible feature of the squamous part of the occipital bone when examining the inferior view of  the skull is a ridge of bone (the external occipital crest), which extends downward from the external occipital protuber-ance toward the foramen magnum. The inferior nuchal lines arc laterally from the midpoint of the crest.
+Immediately lateral to the foramen magnum are the lateral parts of the occipital bones, which contain numer-ous important structural features.
+On each anterolateral border of the foramen magnum are the rounded occipital condyles (Fig. 8.23). These paired structures articulate with the atlas (vertebra CI). Posterior to each condyle is a depression (the condylar fossa) containing a condylar canal, and anterior and superior to each condyle is the large hypoglossal canal. Lateral  to  each  hypoglossal  canal  is  a  large,  irregular jugular foramen formed by opposition of  the jugular notch of  the occipital bone and jugular notch of  the temporal bone.
+
+Temporal bone
+Laterally in the posterior part of the base of the skull is the temporal bone. The parts of the temporal bone seen in this location are the mastoid part of the petromastoid part and the styloid process (Fig. 8.23).
+The lateral edge of the mastoid part is identified by the large  cone-shaped  mastoid  process  projecting  from  its inferior surface. This prominent bony structure is the point of attachment for several muscles. On the medial aspect of the mastoid process is the deep mastoid notch, which is also an attachment point for a muscle.
+Anteromedial  to  the  mastoid  process  is  the  needle-shaped styloid process projecting from the lower border of the temporal bone. The styloid process is also a point of
+attachment for numerous muscles and ligaments.	851
+Head and Neck
+
+
+
+Finally, between the styloid process and the mastoid process is the stylomastoid foramen.
+
+CRANIAL CAVITY
+
+■     the sagittal suture, between the paired parietal bones, and
+■     the lambdoid suture, between the parietal and occipital bones.
+
+
+
+The cranial cavity is the space within the cranium that contains the brain, meninges, proximal parts of the cranial nerves, blood vessels, and cranial venous sinuses.
+
+Roof
+
+Visible junctions of these sutures are the bregma, where the coronal and sagittal sutures meet, and the lambda, where the lambdoid and sagittal sutures meet.
+Other markings on the internal surface of  the calva include bony ridges and numerous grooves and pits.
+
+The  calvaria  is  the  dome-shaped  roof   that  protects	From anterior to posterior, features seen on the bony the superior aspect of the brain. It consists mainly of the       roof of the cranial cavity are:
+
+frontal bone anteriorly, the paired parietal bones in the middle, and the occipital bone posteriorly (Fig. 8.24).
+Sutures visible internally include:
+
+
+■     a midline ridge of bone extending from the surface of the frontal bone (the frontal crest), which is a point of attachment for the falx cerebri (a specialization of the
+
+
+
+■     the coronal suture, between the frontal and parietal bones,
+
+dura mater that partially separates the two cerebral hemispheres);
+
+
+
+
+
+
+
+
+Frontal crest
+
+Frontal bone
+
+
+
+Groove for superior sagittal sinus
+
+
+Bregma
+
+
+Grooves for middle meningeal artery
+
+
+Groove for anterior branch of middle meningeal artery
+
+
+Coronal suture
+
+
+Granular foveolae
+
+
+
+Sagittal suture
+
+
+
+
+
+
+Parietal bone
+
+
+
+
+
+Occipital bone		Lambdoid suture Lambda
+
+852	Fig. 8.24  Roof of the cranial cavity.
+Regional Anatomy  •  Cranial Cavity	8
+
+
+
+■     at the superior point of the termination of the frontal crest the beginning of  the groove for the superior sagittal sinus, which widens and deepens posteriorly and marks the position of the superior sagittal sinus (an intradural venous structure);
+■     on either side of  the groove for the superior sagittal sinus throughout its course, a small number of depres-sions and pits (the granular foveolae), which mark
+
+
+Floor
+The floor of  the cranial cavity is divided into anterior, middle, and posterior cranial fossae.
+
+Anterior cranial fossa
+Parts of the frontal, ethmoid, and sphenoid bones form the anterior cranial fossa (Fig. 8.25). Its floor is composed of:
+
+the  location  of  arachnoid  granulations  (prominent structures readily identifiable when a brain with its meningeal coverings is examined; the arachnoid granu-lations are involved in the reabsorption of cerebrospinal fluid); and
+■     on the lateral aspects of the roof of the cranial cavity, smaller grooves created by various meningeal vessels.
+
+
+■     frontal bone in the anterior and lateral direction, ■     ethmoid bone in the midline, and
+■     two parts of  the sphenoid bone posteriorly, the body (midline) and the lesser wings (laterally).
+
+
+
+
+
+
+
+
+
+
+
+Frontal crest
+Crista galli	Foramen cecum
+
+
+Orbital part (of frontal bone)
+
+
+Foramina of cribriform plate
+
+
+
+
+Cribriform plate (of ethmoid bone)
+
+
+
+Lesser wing (of sphenoid)	Body of (sphenoid) Anterior clinoid process
+
+Fig. 8.25  Anterior cranial fossa.
+
+
+
+
+
+
+
+
+
+
+
+
+
+853
+Head and Neck
+
+
+
+The anterior cranial fossa is above the nasal cavity and the orbits, and it is filled by the frontal lobes of the cerebral hemispheres.
+Anteriorly, a small wedge-shaped midline crest of bone (the frontal crest) projects from the frontal bone. This is a point of attachment for the falx cerebri. Immediately pos-terior to the frontal crest is the foramen cecum (Table 8.2). This foramen between the frontal and ethmoid bones may transmit emissary veins connecting the nasal cavity with the superior sagittal sinus.
+Posterior to the frontal crest is a prominent wedge of bone projecting superiorly from the ethmoid (the crista galli). This is another point of  attachment for the falx cerebri,  which  is  the  vertical  extension  of  dura  mater partially separating the two cerebral hemispheres.
+Lateral to the crista galli is the cribriform plate of the ethmoid bone (Fig. 8.25). This is a sieve-like structure, which allows small olfactory nerve fibers to pass through its foramina from the nasal mucosa to the olfactory bulb. The olfactory nerves are commonly referred to collectively as the olfactory nerve [I].
+On each side of the ethmoid, the floor of the anterior cranial fossa is formed by relatively thin plates of frontal bone (the orbital part of  the frontal bone), which also forms the roof  of  the orbit below. Posterior to both the
+
+frontal and ethmoid bones, the rest of  the floor of  the anterior cranial fossa is formed by the body and lesser wings of the sphenoid. In the midline, the body extends anteriorly between the orbital parts of the frontal bone to reach the ethmoid bone and posteriorly it extends into the middle cranial fossa.
+The boundary between the anterior and middle cranial fossae in the midline is the anterior edge of the prechias-matic sulcus, a smooth groove stretching between the optic canals across the body of the sphenoid.
+
+Lesser wings of the sphenoid
+The two lesser wings of  the sphenoid project laterally from the body of the sphenoid and form a distinct bound-ary between the lateral parts of the anterior and middle cranial fossae.
+Overhanging the anterior part of  the middle cranial fossae, each lesser wing ends laterally as a sharp point at the junction of the frontal bone and the greater wing of the sphenoid near the upper lateral edge of the superior orbital  fissure  that  is  formed  between  the  greater  and lesser wings.
+Medially each lesser wing widens, curves posteriorly, and ends as a rounded anterior clinoid process (Fig. 8.25).  These  processes  serve  as  the  anterior  point  of
+
+
+
+
+
+
+Table 8.2
+
+Foramen
+
+Internal foramina of the skull
+
+Structures passing through foramen
+
+
+
+ANTERIOR CRANIAL FOSSA Foramen cecum
+Olfactory foramen in cribriform plate
+MIDDLE CRANIAL FOSSA Optic canal
+Superior orbital fissure
+
+Foramen rotundum Foramen ovale Foramen spinosum
+Hiatus for the greater petrosal nerve Hiatus for the lesser petrosal nerve
+POSTERIOR CRANIAL FOSSA Foramen magnum
+
+Internal acoustic meatus Jugular foramen
+
+Hypoglossal canal
+854	Condylar canal
+
+
+Emissary veins to nasal cavity Olfactory nerves [I]
+
+Optic nerve [II]; ophthalmic artery
+Oculomotor nerve [III]; trochlear nerve [IV]; ophthalmic division of the trigeminal nerve [V1]; abducent nerve [VI]; ophthalmic veins
+Maxillary division of the trigeminal nerve [V2]
+Mandibular division of the trigeminal nerve [V3]; lesser petrosal nerve Middle meningeal artery
+Greater petrosal nerve Lesser petrosal nerve
+
+End of brainstem/beginning of spinal cord; vertebral arteries; spinal roots of the accessory nerve; meninges
+Facial nerve [VII]; vestibulocochlear nerve [VIII]; labyrinthine artery
+Glossopharyngeal nerve [IX]; vagus nerve [X]; accessory nerve [XI]; inferior petrosal sinus, sigmoid sinus (forming internal jugular vein)
+Hypoglossal nerve [XII]; meningeal branch of the ascending pharyngeal artery
+Emissary vein
+Regional Anatomy  •  Cranial Cavity	8
+
+
+attachment for the tentorium cerebelli, which is a sheet of dura that separates the posterior part of the cerebral hemispheres from the cerebellum. Just anterior to each
+
+Sella turcica
+Just posterior to the chiasmatic sulcus is the uniquely modified remainder of the body of the sphenoid (the sella
+
+anterior clinoid process is a circular opening in the lesser	turcica),  which  consists  of  a  deep  central  area  (the
+
+wing of the sphenoid (the optic canal), through which the ophthalmic artery and optic nerve [II] pass as they exit the cranial cavity to enter the orbit. The optic canals are usually included in the middle cranial fossa.
+
+Middle cranial fossa
+The middle cranial fossa consists of parts of the sphenoid and temporal bones (Fig. 8.26).
+The boundary between the anterior and middle cranial fossae in the midline is the anterior edge of the prechias-
+
+hypophyseal fossa) containing the pituitary gland with anterior and posterior vertical walls of bone (Fig. 8.26).
+The anterior wall of  the sella is vertical in position with its superior extent visible as a slight elevation (the tuberculum sellae) at the posterior edge of  the chias-matic sulcus.
+Lateral projections from the corners of the tuberculum sellae  (the  middle  clinoid  processes)  are  sometimes evident.
+The posterior wall of the sella turcica is the dorsum
+
+matic sulcus, which is a smooth groove stretching between       sellae,  a  large  ridge  of  bone  projecting  upward  and the optic canals across the body of the sphenoid.                      forward. At the top of  this bony ridge the lateral edges The posterior boundaries of the middle cranial fossa are       contain  rounded  projections  (the  posterior   clinoid
+
+formed by the anterior surface, as high as the superior border, of the petrous part of the petromastoid part of the temporal bone.
+
+Sphenoid
+The floor in the midline of the middle cranial fossa is ele-vated and formed by the body of the sphenoid. Lateral to this are large depressions formed on either side by the greater wing of the sphenoid and the squamous part of the temporal bone. These depressions contain the temporal lobes of the brain.
+
+processes),  which  are  points  of  attachment,  like  the anterior clinoid processes, for the tentorium cerebelli.
+
+Fissures and foramina
+Lateral to each side of the body of the sphenoid, the floor of the middle cranial fossa is formed on either side by the greater wing of the sphenoid (Fig. 8.26).
+A diagonal gap, the superior orbital fissure, separates the greater wing of  the sphenoid from the lesser wing and is a major passageway between the middle cranial fossa and the orbit. Passing through the fissure are the
+
+
+
+
+
+
+Prechiasmatic sulcus Tuberculum sellae
+
+Middle clinoid process Optic canal
+Foramen rotundum Superior orbital fissure
+Greater wing (of sphenoid)
+
+
+
+
+
+Hypophyseal fossa
+
+
+Posterior clinoid process
+
+Groove and hiatus for lesser petrosal nerve
+
+Tegmen tympani
+
+
+
+
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