372 A MANUAL OF ANATOMY 



radialis indicis and arteria princeps pollicis of the radial. As the 

 digital arteries pass towards the fingers they lie between the flexor 

 tendons, and superficial to the digital nerves and lumbricales 

 muscles. Along the sides of the fingers, however, the digital 

 nerves are superficial to the arteries. Just before the outer three 

 digital arteries divide into their collateral branches each is joined 

 by a palmar interosseous artery from the deep palmar arch, and, 

 it may be, by the inferior perforating branches of the dorsal inter- 

 osseous arteries. The innermost digital artery receives its com- 

 municating branch from the innermost palmar interosseous about 

 the centre of the hand. As the arteries pass along the sides 

 of the fingers they anastomose with each other across the front 

 of the phalanges to form arches, which are placed on the proximal 

 side of the interphalangeal joints. Each also supplies the flexor 

 tendons with their sheaths, and gives off a few dorsal branches. 

 In front of each terminal phalanx the arteries of each finger unite to 

 form an arch, from which many twigs are given off to supply the 

 pulp of the finger and matrix of the nail. 



The varieties of the superficial palmar arch will be afterwards 

 described. 



Veins. — The superficial palmar arch is accompanied by two 

 venae comites, and so are the digital arteries. The venae comites 

 of the digital arteries unite at the clefts of the fingers to form 

 single vessels, and these end in the venae comites of the superficial 

 palmar arch. The venae comites of the inner part of the arch unite, 

 and so do those of the inner part of the deep palmar arch, and in 

 this way the venae comites of the ulnar artery are formed. Those 

 from the outer side of the superficial arch go with the superficial 

 volar artery, and, with those from the outer side of the deep arch 

 which accompany the second part of the radial artery, form the 

 radial venae comites. 



Median Nerve in the Hand. — The median nerve enters the palm 

 by passing beneath the anterior annular ligament, where it lies 

 within the great palmar bursa along with the superficial and deep 

 flexor tendons, giving off articular twigs to the wrist- joint. Close 

 to the lower border of the ligament it presents an enlargement, 

 and breaks up into two divisions — external and internal. The 

 external division gives off a muscular branch and three single 

 digital nerves. The muscular branch passes outwards, and divides 

 to supply the abductor pollicis, opponens pollicis, and superficial 

 head of the flexor brevis pollicis. The three single digital nerves 

 are distributed to the outer and inner sides of the thumb and the 

 outer side of the index finger, and the latter nerve gives a l)ranch 

 to the first, or most external, lumbricalis. The internal division 

 breaks up into two compound digital nerves. The outer of these 

 passes to near the cleft between the index and middle fingers, 

 where it divides into two collateral digital nerves for the supply of 

 the contiguous sides of these fingers. In its course it gives a branch 

 to the second lumbricalis. The inner passes to near the cleft 



