MEDIAN NEKVE. 705 



the seventh or sixth and seventh nerves. It is usually double, one branch entering 

 each portion of the muscle. The lateral cutaneous nerve of the forearm divides into 

 volar and dorsal branches (Fig. 616, p. 704). The volar branch runs distally along 

 the front of the lateral aspect of the forearm to the wrist, and supplies an area 

 extending medially to the middle line of the forearm anteriorly, and distally so 

 as to include the ball of the thumb. It communicates, proximal to the wrist, 

 with the superficial ramus of the radial nerve, and supplies branches to the 

 radial artery. The dorsal branch passes backwards and distally over the extensor 

 muscles and supplies the skin on the lateral aspect of the forearm posteriorly in 

 its proximal three-fourths, communicating with the cutaneous branches of the 

 radial nerve. 



In addition to the above branches, the musculo-cutaneous nerve supplies in many 

 cases the following small twigs in the arm : (1) a medullary branch to the humerus ; (2) 

 a periosteal branch to the distal erid of the humerus on its anterior surface ; and (3) a 

 branch to the brachial artery. 



NERVUS MEDIANUS. 



The median nerve arises by two heads one from the lateral cord, the other 

 from the medial cord of the brachial plexus. The lateral head, from the (fifth), 

 sixth, and seventh nerves, descends along the lateral side of the axillary artery ; 

 the medial head, from the eighth cervical and first thoracic nerves, crosses the 

 end of the axillary artery or the beginning of the brachial artery, to join the other 

 head in the proximal part of the arm. Descending along the lateral aspect of the 

 brachial artery, the nerve crosses over it obliquely in the distal half of the arm. In 

 the hollow of the elbow, it lies on the medial side of the brachial artery, behind the 

 lacertus fibrosus and the median basilic vein. It passes into the forearm between 

 the two heads of the pronator teres muscle, separated from the ulnar artery by the 

 deep origin of that muscle. Extending distally along the middle of the forearm, 

 between the superficial and deep muscles, to the wrist, it enters the palm of the hand 

 on the lateral side of the flexor tendons of the fingers, and deep to the transverse 

 carpal ligament. In the hand, it spreads out at the distal border of the transverse 

 carpal ligament, under cover of the palmar aponeurosis and superficial volar arch, 

 and separates into its six terminal branches. In the forearm a small artery accom- 

 panies it, the median branch of the volar interosseous artery. Immediately 

 proximal to the wrist it is comparatively superficial, lying on the lateral side of the 

 superficial flexor tendons and directly behind the tendon of the palmaris longus. 



Branches. The median nerve usually gives off no branches in the (upper) 

 arm. 



Branches in the Forearm. (1) Articular Branches. Minute articular filaments 

 are distributed to the front of the elbow-joint. 



(2) Muscular Branches. Just below the elbow a bundle of nerves arises to be 

 distributed to the following muscles : pronator teres, flexor carpi radian's, palmaris 

 longus, flexor digitorum sublimis. Nerves are also generally traceable from this 

 bundle to the upper fibres of the flexor pollicis longus and flexor digitorum 

 profundus. The nerve to the pronator teres often arises independently in the 

 hollow of the elbow. 



(3) The volar interosseous nerve of the forearm (O.T. anterior interosseous) arises 

 from the posterior surface of the median nerve in the forearm. It passes distally on 

 the volar aspect of the interosseous membrane along with the volar interosseous 

 artery, lies dorsal to the pronator quadratus muscle, and terminates by supplying 

 articular filaments to the radio-carpal articulation. In its course the nerve supplies 

 muscular branches to the flexor pollicis longus, the lateral half of the flexor 

 digitorum profundus, and the pronator quadratus, minute medullary branches to 

 the radius and ulna, and twigs to the periosteum and interosseous membrane. 



(4) Palmar Eamus. In the distal third of the forearm a small cutaneous 

 branch arises, which pierces the deep fascia and crosses the transverse carpal 

 ligament to reach the palm of the hand. It supplies the skin of the palm and com- 



46 



