928 THE NERVOUS SYSTEM 



fossa it lies external to the axillary artery and it is overlapped, on its outer side, by 

 thecoraco-brachialis muscle. In the upper half of the arm it lies along the outer side of 

 the brachial artery, and it is overlapped by the inner border of the biceps. At the 

 middle of the arm it passes in front of the brachial artery, and then it descends, on the 

 inner side of the artery, to the elbow. In the upper part of the antecubital fossa 

 it is still at the inner side of the brachial artery, but separated from it by a small 

 interval, and in the lower part of the fossa it lies along the inner side of the ulnar 

 artery. As it leaves the antecubital fossa it passes between the two heads of the 

 pronator teres, and it crosses in front of the ulnar artery (fig. 683), from which it is 

 separated by the deep head of the pronator. In the forearm it passes vertically 

 downwards, accompanied by the median (comes nervi mediani) artery. In the upper 

 two-thirds of the region it lies deeply, between the flexor digitorum sublimis and 

 the flexor digitorum profundus, but in the lower third it becomes more superficial, 

 and is placed beneath the deep fascia, between the flexor carpi radialis on the radial 

 side and the palmaris longus and flexor digitorum sublimis tendons on the ulnar 

 side. It crosses beneath the transverse carpal (anterior annular) ligament, in front 

 of the flexor tendons, and in the palm at the lower border of the ligament it enlarges 

 and divides into three branches, the common volar digital nerves. 



Branches. The median nerve does not supply any part of the upper arm.. In 

 front of the elbow-joint it furnishes one or two filaments to that articulation. In 

 the forearm it supplies all the superficial anterior muscles (with the exception of 

 the flexor carpi ulnaris) directly from its trunk, and it supplies the deep muscles 

 (with the exception of the inner half of the flexor digitorum profundus) by the volar 

 (anterior) interosseous branch. In the hand it supplies the group of short muscles 

 of the thumb which are placed on the radial side of the tendon of the flexor pollicis 

 longus, the two outer lumbricales, the integument covering the central part of the 

 palm and inner part of the thenar eminence, and the palmar aspect of the first, 

 second, third, and radial half of the fourth digits. It also sends twigs to the dorsal 

 aspect of these digits. 



The nerve to the pronator teres usually arises a little above the bend of the 

 elbow, and pierces the outer border of the muscle (figs. 683 and 684). It may arise 

 in a common trunk with the following nerves: 



The nerves to the flexor carpi radialis, palmaris longus, and flexor digitorum 

 sublimis arise a little lower down, and pierce the pronator-flexor mass of muscles to 

 end in the respective members of the group for which they are destined (fig. 682) . 



The volar (anterior) interosseous nerve arises from the median at the level of the 

 bicipital tubercle of the radius (fig. 683) , and runs downwards, on the interosseous 

 membrane, accompanied by the volar (anterior) interosseous artery. It passes under 

 cover of the pronator quadratus, and pierces the deep surface of that muscle, which it 

 supplies. The volar interosseous nerve also furnishes a twig to the front of the wrist- 

 joint, and supplies the flexor digitorum profundus and the flexor pollicis longus. The 

 nerve to the former muscle arises from the volar interosseous near its commencement ; 

 it supplies the outer two divisions of the muscle, and it communicates within the 

 substance of the muscle with twigs derived from the ulnar nerve. 



It also supplies a branch to the interosseous membrane which runs downwards 

 upon, or in, the membrane, supplying it and giving branches to the volar (anterior) 

 interosseous and nutrient arteries and to the periosteum of the radius, the ulna, and 

 the carpus. 



The palmar cutaneous branch arises immediately above the transverse carpal 

 (anterior annular) ligament and passes between the tendons of the flexor carpi 

 radialis and the palmaris longus (fig. 683) . It then crosses the superficial surface of 

 the transverse carpal ligament, and is distributed to the integument and fascia on the 

 central depressed surface of the palm. It also supplies a few twigs to the inner border 

 of the thenar eminence; these twigs communicate with the musculo-cutaneous and 

 superficial radial nerves. 



The three common volar digital nerves pass in the palm of the hand dorsal 

 to the superficial palmar arch and its digital branches, while the proper volar 

 digitals, branches of these nerves, lie ventral to the digital arteries. 



The first of the common volar digital nerves gives off a branch to supply the 

 abductor pollicis, the opponens, and the superficial head of the flexor pollicis brevis, 

 and anastomoses by a delicate branch with the deep branch of the ulnar nerve. It 

 then divides into three proper volar digitals (fig. 684). The outer of these passes 



