6o 



THE NERVOUS SYSTEM 



If, as seems probable, the musculature of the extremities has not developed 

 along metameric lines, there can be no true metamerism of the motor nerves to 

 the limbs (Streeter, 1912). Yet the fibers from each ventral root are distributed 

 in a very orderly manner. As is indicated in the table on page 77, almost every 

 long muscle receives fibers from two or more ventral roots. It will be apparent 

 that the muscles of the trunk are innervated from the roots belonging to the 



Great auricular 

 Cutaneous nerve of the neck 

 Supraclavicular nerves 

 Axillary 



Intercostobrachial 

 Medial cutaneous of arm 

 Posterior cutaneous of arm 

 Medial cutaneous of forearm 

 Musculocutaneous 



Radial 

 Median 

 Ulnar 



Genitofemoral ' 



Lateral cutaneous of the thigh' 

 Intermediate cutaneous rami' 

 Medial cutaneous rami 

 Infrapatellar ramus 

 Lateral sural 

 Saphenous 

 Superficial peroneal 

 Sural 

 Deep peroneal 



Fig. 36. Sensory root fields on the right, contrasted with the areas of distribution of cutaneous 



nerves on the left. 



several metameres from the myotomes of which these muscles * developed. The 

 table shows in a general way the distribution of the fibers of the several ventral 

 roots. 



Functional Classification of Nerve-fibers. Many years ago Sir Charles 

 Bell (1811, 1844) showed that the dorsal roots are sensory in function and the 

 ventral roots motor; and this has been known since then as Bell's law. He 

 recognized that sensory and motor fibers are distributed to the viscera as well as 



