96 THE UPPER EXTREMITY 



superficial division of the radial nerve, but from that branch 

 of it which goes to the lateral margin of the thumb. It is 

 joined by a twig from the lateral cutaneous nerve of the 

 forearm, and proceeds downwards in front of the tendon 

 of the abductor pollicis longus to end in the skin covering 

 the ball of the thumb (Fig. 27, p. 66). 



Dissection. In tracing the nerves which appear on the dorsum of the 

 forearm, it will be necessary to remove the skin from the dorsal aspect of 

 the thumb and fingers. The great flap of skin which is still attached at 

 the roots of the fingers may be detached, and an incision can then be made 

 along the middle of the dorsal aspect of each digit. The skin should be 

 carefully raised from each finger in two flaps and thrown laterally and 

 medially. 



Nervi Cutanei Dorsales (Dorsal Cutaneous Nerves). 

 The dorsal branch of the ulnar nerve winds round the medial 

 margin of the wrist to reach the dorsum of the hand. It 

 will be found immediately below the prominence formed by 

 the distal end of the ulna, and it at once divides into three 

 main terminal branches. Of these, one runs along the ulnar 

 margin of the dorsum of the hand, and is continued onwards 

 along the medial margin of the little finger. The second 

 branch proceeds towards the cleft between the little finger 

 and the ring finger, and divides into two twigs which supply 

 the contiguous sides of these digits. The third branch joins 

 a twig from the superficial branch of the radial nerve, and 

 the nerve thus formed runs towards the interval between the 

 ring finger and the middle finger, and divides to supply 

 their adjacent margins. Each of these three main branches 

 gives several minute filaments to the integument on the 

 dorsum of the hand (Fig. 28, p. 68). 



The superficial branch of the radial nerve will be found 

 winding round the lateral margin of the forearm, about two 

 inches proximal to the extremity of the styloid process of the 

 radius. It at once gives off a long twig which proceeds along 

 the radial margin of the hand and thumb. A little farther on 

 it breaks up into four terminal branches, which are distributed 

 as follows : the first supplies the medial side of the thumb ; 

 the second goes to the lateral side of the index finger; the 

 third divides to supply the adjacent sides of the index and 

 middle fingers ; whilst the fourth joins with a twig from the 

 dorsal branch of the ulnar (as already described) to supply 

 the contiguous margins of the middle and ring fingers. 



