FOREARM AND HAND 173 



intermediate area the distal branch of the dorsal cutaneous 

 nerve of the forearm ; (4) the superficial division of the radial 

 nerve appearing from under cover of the brachio - radialis 

 about 8 cm. (3^ inches) proximal to the wrist. Thus three of 

 the terminal branches of the brachial plexus are represented 

 on the dorsum of the forearm the musculo-cutaneous nerve 

 by the lateral cutaneous nerve of the forearm ; the medial 

 cutaneous nerve of the forearm ; and the radial nerve by 

 its superficial division, and by the dorsal cutaneous nerve 

 of the forearm. 



In the dorsum of the hand the distribution of the super- 

 ficial branch of the radial nerve and the dorsal branch of 

 the ulnar nerve have already been examined (pp. 71, 72); 

 the radial nerve supplies the greater part of the skin of 

 the dorsum of the hand and three and a half digits the 

 thumb, and the proximal parts of the index, the middle, 

 and half the ring fingers whilst the dorsal branch of the 

 ulnar nerve supplies the remaining half of the ring finger and 

 the little finger. The skin of the distal parts of the index, 

 the middle, and half the ring fingers is supplied, as already 

 noted (p. 159), by twigs of the digital branches of the 

 median nerve. 



Dissection. Remove the cutaneous vessels and nerves from 

 the dorsum of the forearm and hand, then revise the deep fascia. 



The Deep Fascia. The deep fascia of the dorsum of the 

 forearm is stronger than the deep fascia of the volar aspect. 

 Its proximal part is strengthened by expansion from the 

 triceps, and near the elbow it is intimately connected with 

 the muscles of the back of the forearm which take part 

 of their origin from its deep surface. It is closely attached 

 to the whole length of the dorsal border of the ulna, and 

 in the regions of the distal ends of the radius and ulna and 

 the back of the carpus it is thickened by numerous trans- 

 verse fibres which constitute the ligamentum carpi dorsale. 



Dissection. The dorsal carpal ligament must be left in situ 

 until the dissection of the dorsal parts of the forearm and hand 

 is completed. To secure its retention in an uninjured condition, 

 isolate it by cutting carefully through the deep fascia parallel with 

 its proximal border. Whilst making the incision, care must be 

 taken to avoid injury to the mucous sheaths of the extensor 

 tendons which lie immediately subjacent to the deep fascia. 

 When the front of the forearm was dissected, the radial flap of 

 deep fascia was reflected only as far as the radial border of the 



