158 THE NERVOUS SYSTEM 



limb increases in size, the sixth and seventh cervical nerves 

 reach the pre-axial border and the eighth reaches the post- 

 axial border (Fig. 68). 



This arrangement is maintained throughout development. 

 In Fig. 67 the segmental distribution of the cutaneous nerves 

 of the upper limb is represented diagrammatically. The fifth 

 and sixth cervical nerves supply the lateral aspect of the arm 

 and forearm ; while the seventh does not appear on the 

 volar aspect till the hand is reached. The medial aspect 

 of the limb is supplied by the eighth cervical and the first 

 and second thoracic nerves. On the dorsal aspect of the 



C4 

 C5 

 C 6 

 C 7 



ce 



X T2 



Stage I. Stage II. 



FIG. 68. Diagram representing the development of the Upper Limb, and 

 the segmental arrangement of its Sensory Nerve-supply. 



limb, the arrangement is precisely similar except that the 

 seventh cervical nerve reaches the skin of the forearm. This 

 description is in harmony with the views of Edinger, Purves- 

 Stewart and others, but it is not accepted by Sherren, who 

 holds that the whole of the lateral aspect of the limb is 

 supplied by the fifth, sixth and seventh cervical nerves and 

 that the areas supplied by each are practically co-extensive. 



LESIONS OF THE BRACHIAL PLEXUS 



In accordance with the segmental motor and sensory supply 

 of the upper limb, it is possible to determine the exact site 

 of injuries of the spinal medulla or of the anterior rami of 

 the spinal nerves in the lower cervical region. Injuries of 



