SPINAL NERVES. 



757 



deeply seated branch of the median, coming 

 off at an acute angle from the trunk, between 

 the origin of the deep-seated muscular brandies. 

 It runs vertically downwards in company with, 

 but to the radial side of, the corresponding 

 artery, in front of the interosseous membrane 

 between the flexor digitorum profundus and 

 flexor longus pollicis, giving on either side 

 small filaments to them. Having reached the 

 upper edge of the pronator quadratus, it 

 passes behind that muscle, and terminates 

 either by sending numerous filaments into its 

 posterior surface, or, after having supplied it, 

 perforates the lower aperture of the interos- 

 seous membrane, and reaches the back of the 

 carpus. 



The palmar cutaneous branch is given off at 

 the lower fourth of the fore-arm, passes for- 

 wards from beneath the tendons of the flexor 

 sublimis, and behind the fascia, which it per- 

 forates a little above the wrist, and divides 

 into an external filament, which, having com- 

 municated with the radial, terminates in the 

 skin of the vola major, and an internal de- 

 scending over the annular ligament to be lost 

 in the skin of the upper part of the palm. 



The terminal digital branches of the median 

 are derived from two primary branches, into 

 which the flattened and expanded nerve di- 

 vides, after having passed from beneath the 

 annular ligament. These are external and 

 internal, the former supplying the muscles of 

 the thumb, and sending off three digital 

 branches for the thumb and radial side of the 

 index finger, and rather smaller than the 

 latter, which gives off two digital branches 

 for the opposed sides of the index and middle, 

 and the middle and ring finger. The muscular 

 branch passes in a slightly curved manner out- 

 wards and upwards, and terminates in fila- 

 ments for the supply of the abductor, opponens 

 and flexor brevis pollicis. 



The first digital nerve is directed obliquely 

 downwards and outwards in front of the 

 tendon of the flexor longus pollicis, and near 

 the head of the metacarpal bone, crosses it 

 to its outer side, and continues its course to 

 the extremity of the outer side of the anterior 

 aspect of the first phalanx, where it terminates 

 in dorsal and palmar branches. The dorsal 

 branch winds on to the back of the last pha- 

 lanx, communicates with the radial, and sup- 

 plies the skin at the root of the nail ; the 

 palmar continues in the original course of 

 the nerve to the skin at the extremity of the 

 thumb. 



The second digital nerve, not so oblique 

 in its direction as the first, crosses over the 

 adductor pollicis, gives a filament to it, and 

 is conducted along the inner side of the flexor 

 longus pollicis tendon to the ulnar side of 

 the thumb, sending in its course some fila- 

 ments backwards to communicate with the 

 dorsal branches of the radial, and terminating 

 in a similar manner to the preceding branch. 



The third digital nerve is directed in front, 

 and to the outside of the first lumbrical 

 muscle, gives a filament to it, and reaches to 

 about the middle of the outer side of the 



proximal phalanx of the index finger, where 

 it divides into dorsal and palmar branches. 

 The dorsal branch passes on to the back of 

 the phalanx, communicates with one of the 

 dorsal cutaneous nerves, to form a nerve which 

 ends in the integuments of the back part of 

 the last phalanx : the palmar branch passes 

 in the original direction of the nerve, and 

 terminates on the outer side of the distal pha- 

 lanx by again dividing into palmar and dorsal 

 branches, having a similar distribution to the 

 two first nerves. 



The fourth digital nerve passes in front of 

 the second interosseous space, gives a filament 

 to the second lumbrical muscle, and about 

 the middle of this space divides into two 

 branches, which are directed along the op- 

 posed sides of the middle and index fingers. 

 The fifth passes downwards and slightly in- 

 wards in front of the third metacarpal space, 

 gives a filament to the third lumbricus, com- 

 municates by a delicate filament with the 

 ulnar, and at the middle of this space ter- 

 minates in two branches for the opposed sides 

 of the middle and ring finger. The termina- 

 tion of the divisions of the fourth and fifth 

 digital nerves, and the branches given off from 

 them, are exactly similar in distribution to 

 the third digital nerve, giving off, like it, on 

 the proximal and distal phalanx, a dorsal 

 branch. Each of the digital nerves, although 

 running along the sides of the fingers, and 

 giving off in their course numerous cutaneous 

 filaments, which are directed towards the axes 

 of the fingers, are not observed to anastomose 

 with each other. 



The median nerve in the palm of the hand 

 is situated on a plane anterior to all the 

 flexor tendons, and the trunk before dividing 

 is situated half an inch or more above the 

 level of the superficial palmar arch of arteries 

 which crosses in front of its three internal 

 branches. The accompanying digital arteries 

 are placed somewhat behind, and further from 

 the longitudinal axes of the fingers than the 

 nerves, which, however, in their course send 

 numerous small filaments which wind around 

 them. 



The ulnar nerve t somewhat smaller than 

 the median, arises from a trunk common to 

 it, the internal cutaneous and the inner head 

 of the median. The first dorsal and last cer- 

 vical are consequently principally engaged in 

 forming it. Almost immediately after its 

 origin it is directed slightly inwards and out- 

 wards from the median, and behind the in- 

 ternal cutaneous, and at the lower part of 

 the axilla appears deeply seated at the inner 

 aspect of the arm, being directed in front of 

 the triceps extensor muscle. Below the level 

 of the coraco-brachialis it perforates the in- 

 ternal intermuscular septum, and becomes 

 surrounded by several fasciculi, derived from 

 the inner head of the triceps, and passes be- 

 hind the intermuscular septum to gain the 

 space between the internal condyle and ole- 

 cranon, being here situated between the two 

 heads of the flexor carpi ulnaris. It now in- 

 clines downwards and slightly outwards along 



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