350 A MANUAL OF ANATOMY 



by the radial nerve and the dorsal branch of the ulnar. The 

 radial nerve winds backwards beneath the tendon of the brachio- 

 radialis about 3 inches above the wrist, and then divides into two 

 branches — external and internal. The external branch passes to 

 supply the outer side of the thumb, giving off in its course the 

 palmar cutaneous branch. The internal branch, having com- 

 municated with the posterior branch of the musculo-cutaneous, and 

 having given a branch to the back of the wrist which communicates 

 with the dorsal branch of the ulnar, divides into four digital nerves. 

 The first supplies the inner side of the thumb, the second the outer 

 side of the index finger, the third bifurcates at the cleft between the 

 index and middle fingers into two collateral branches for the supply 

 of their contiguous sides, and the fourth passes to the cleft between 

 the middle and ring fingers. The latter in its course is reinforced 

 by an offset from the dorsal branch of the ulnar, and then it divides 

 into two collateral nerves for the supply of the contiguous sides of 

 the middle and ring fingers. 



The dorsal branch of the ulnar nerve arises about 2^ inches 

 above the wrist, and winds backwards beneath the tendon of the 

 flexor carpi ulnaris. It then gives a branch to the back of the 

 wrist, which communicates with a branch of the radial, and there- 

 after is distributed as follows : one branch supplies the inner 

 side of the little finger ; a second branch passes to the cleft 

 between the little and ring fingers, giving an offset to the innermost 

 digital branch of the radial, and it divides into two collateral 

 branches for the supply of the contiguous sides of these fingers ; 

 whilst a third branch is distributed to the integument of the back 

 of the hand. 



The distribution of the dorsal digital nerves is as follows : on the 

 thmnb they extend as far as the nail, on the index finger to the 

 distal end of the second phalanx, on the middle finger to near the 

 distal end of the first phalanx, on the ring-finger to near the distal 

 end of the second phalanx, and on the little finger as far as the 

 nail. The portions of integument not supplied by the dorsal 

 digital nerves derive their innervation from branches which pass 

 backwards from the palmar digital branches" of the median and 

 ulnar nerves. 



Veins. — ^The superficial veins of the forearm, already described, 

 are the radial, median, anterior ulnar, and posterior ulnar. On the 

 back of the hand is the dorsal venous plexus, and in front of the 

 anterior annular ligament is the anterior plexus, of small size. The 

 dorsal venous plexus receives the superficial digital veins, which com- 

 mence in plexuses in the region of the nails. They are two in number 

 to each finger, one being placed on each side towards the dorsal 

 aspect. These veins form cross arches above and below the inter- 

 phalangeal joints on the backs of the fingers. At the clefts the 

 collateral veins unite to form in each case a single trunk, and these 

 trunks end in the dorsal venous plexus. The superficial digital 

 vein from the inner side of the little finger passes to the commence- 



