938 NEUROLOGY 



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The Median Nerve (n. medianus) (Fig. 816) extends along the middle of the ana 

 and forearm to the hand. It arises by two roots, one from the lateral and one from 

 the medial cord of the brachial plexus; these embrace the lower part of the axillary 

 artery, uniting either in front of or lateral to that vessel. Its fibers are derived 

 from the sixth, seventh, and eighth cervical and first thoracic nerves. As it descends 

 through the arm, it lies at first lateral to the brachial artery; about the level of the 

 insertion of the Coracobrachialis it crosses the artery, usually in front of, but occasion- 

 ally behind it, and lies on its medial side at the bend of the elbow, where it is situated 

 behind the lacertus fibrosus (bicipital fascia) , and is separated from the elbow-joint 

 by the Brachialis. In the forearm it passes between the two heads of the Pronator 

 teres and crosses the ulnar artery, but is separated from this vessel by the deep 

 head of the Pronator teres. It descends beneath the Flexor digitorum sublimis, 

 lying on the Flexor digitorum profundus, to within 5 cm. of the transverse carpal 

 ligament; here it becomes more superficial, and is situated between the tendons of 

 the Flexor digitorum sublimis and Flexor carpi radialis. In this situation it lies 

 behind, and rather to the radial side of, the tendon of the Palmaris longus, and is 

 covered by the skin and fascia. It then passes behind the transverse carpal liga- 

 ment into the palm of the hand. In its course through the forearm it is accompanied 

 by the median artery, a branch of the volar interroseous artery. 



Branches. With the exception of the nerve to the Pronator teres, which some- 

 times arises above the elbow-joint, the median nerve gives off no branches in 

 the arm. As it passes in front of the elbow, it supplies one or two twigs to the 

 joint. 



In the forearm its branches are : muscular, volar interosseous, and palmar. 



The muscular branches (rami musculares) are derived from the nerve near the 

 elbow and supply all the superficial muscles on the front of the forearm, except 

 the Flexor carpi ulnaris. 



The volar interosseous nerve (n. interosseus [antibrachii] wlaris; anterior inter- 

 osseous nerve) supplies the deep muscles on the front of the forearm, except the ulnar 

 half of the Flexor digitorum profundus. It accompanies the volar interosseous 

 artery along the front of the interosseous membrane, in the interval between the 

 Flexor pollicis longus and Flexor digitorum profundus, supplying the whole of the 

 former and the radial half of the latter, and ending below in the Pronator quadratus 

 and wrist-joint. 



The palmar branch (ramus cutaneus palmaris n. mediani) of the median nerve arises 

 at the lower part of the forearm. It pierces the volar carpal ligament, and divides into 

 a lateral and a medial branch; the lateral branch supplies the skin over the ball of 

 the thumb, and communicates with the volar branch of the lateral antibrachial 

 cutaneous nerve; the medial branch supplies the skin of the palm and communi- 

 cates with the palmar cutaneous branch of the ulnar. 



In the palm of the hand the median nerve is covered by the skin and the palmar 

 aponeurosis, and rests on the tendons of the Flexor muscles. Immediately after 

 emerging from under the transverse carpal ligament the nerve becomes enlarged 

 and flattened and splits into a smaller, lateral, and a larger, medial portion. The 

 lateral portion supplies a short, stout branch to certain of the muscles of the ball of 

 the thumb, viz., the Abductor brevis, the Opponens, and the superficial head of the 

 Flexor brevis, and then divides into three proper volar digital nerves; two of these 

 supply the sides of the thumb, while the third gives a twig to the first Lumbricalis 

 and is distributed to the radial side of the index finger. The medial portion of the 

 nerve divides into two common volar digital nerves. The first of these gives a twig 

 to the second Lumbricalis and runs toward the cleft between the index and middle 

 fingers, where it divides into two proper digital nerves for the adjoining sides of 

 these digits; the second runs toward the cleft between the middle and ring fingers, 

 and splits into two proper digital nerves for the adjoining sides of these digits; 



