992 THE NERVOUS SYSTEM 



along the medial side of the ulnar artery. In case of the high division of the brachial artery, 

 when the radial and the ulnar arteries he together in the upper arm, the median nerve may pass 

 between them and then one or the other of the arteries will be superficial to the nerve. 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. 759), from which it is separated by the deep head of the 

 pronator. In the forearm it passes vertically downward, accompanied by the median (comes 

 nervi mediani) artery. In the upper two-thirds of this 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 (fig. 760). 



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 ulnar half of the flexor digitorum profundus) 

 by its volar (anterior) interosseous branch. Thus in general it supplies the 

 pronator and flexor muscles of the forearm (radial side). 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 lateral lumbricales, the integument 

 covering the central part of the palm and ulnar aspect 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 lateral border of the muscle (figs. 759 and 761). 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 httle 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. 758). 



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

 tubercle of the radius (fig. 759), and runs downward, on the interosseous membrane, accom- 

 panied by the volar (anterior) interosseous artery. It passes under cover of the pronator quad- 

 ratus, 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 downward 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. 759). 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 medial border of the thenar eminence; these twigs commu- 

 nicate 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 on the volar side of tlic digital arteries. 



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

 pollicis, the opi)onens, and the superficial head of the flexor pollicis brevis, and joins by a delicate 

 branch with the deep branch of the ulnar nerve. It then divides into three proper volar digitals 

 (fig. 761). The lateral of these passes obliquely across the long flexor tendon of the thumb and 

 runs along the radial border of the thumb to its extremity. It gives numerous branches to the 

 pulp of the thumb, and a strong twig which passes to the dorsum to supply the matrix of the 

 nail. The second of these proper volar digitals supplies the medial side of the volar aspect of 

 the thumb and gives off a twig to the matrix of the thumb nail. The third supplies the radial 

 side of the second digit and gives a twig to the first lumbrical muscle. 



The second coiiimon volar digital sends a twig to the second lumbrical nuisclo, and divides 

 a little abcjve tlie m(!ta(-ari)o-])lialangeal articulation into two proper volar digitals, which 

 respectively supply the adjacent sides of the second and third digits. 



The third common volar digital communicates with the ulnar nerve, often gives a branch 

 to the third lumbrical muscle, and divides into two proper volar digitals which supply the adja- 

 cent sides of the third and fourth digits. 



As the proper volar digitals pass along the margins of tlie fingers they give off twigs for 

 the innervation of the skin on the dorsum of tlie second and third phalanges and the matrix 

 of their nails. I'iach of the nerves terminates in filaments to the pulp of the finger. 



