142 THE NERVOUS SYSTEM 



radialis does not produce any special attitude, but, as all the 

 extensors of the wrist and fingers are involved, the wrist and 

 ringers are maintained in a position of flexion by the tonus of 

 their flexor muscles. At the same time, it should be remem- 

 bered that the lumbricals and interossei (p. 145) are able to 

 extend the interphalangeal joints of the medial four digits, and 

 care must be taken not to assume that such a movement, 

 occurring during an endeavour to extend the fingers and wrist, 

 is produced by the extensor muscles. 



When the radial (musculo-spiral) nerve is divided distal to 

 the point of origin of the dorsal cutaneous nerve of the fore- 

 arm> there is no appreciable loss of sensibility in the forearm 

 or hand, on account of the communications which exist between 

 the superficial branch and the adjoining nerves (p. 141). If 

 the radial nerve is divided proximal to the point of origin 

 of the dorsal cutaneous nerve of the forearm^ the sensory loss 

 involves the radial side of the dorsum of the hand. The fore- 

 arm is not affected, owing to the overlapping of the dorsal 

 cutaneous nerve by the lateral and medial cutaneous nerves of 

 the forearm. Both epicritic and protopathic sensibilities are 

 lost over the radial half of the dorsum of the hand and over 

 the dorsal aspect of the first phalanx of the thumb, but, owing 

 to overlapping by the volar (palmar) digital nerves, the second, 

 third and fourth digits are not affected. 



The superficial branch of the radial nerve establishes its 

 communications in the distal third of the forearm, and, when 

 it is injured in this part of its course, some loss of sensibility 

 may be discovered on the dorsum of the hand. 



(C) The Medial Cord (C. 8 and T. i). The Medial 

 Anterior Thoracic Nerve supplies the pectoralis minor and 

 assists the lateral anterior thoracic nerve to supply the 

 pectoralis major (p. 133). 



The pectoralis minor lies under cover of the major and 

 extends from the sternal ends of the third, fourth and fifth ribs 

 to the coracoid process of the scapula. When it contracts, it 

 draws the point of the shoulder downwards and forwards ; or, 



