THE NERVOUS SYSTEM 



373 



The visceral motor fibers which appear in the dorsal roots of lower 

 vertebrates are not found in the dorsal spinal nerves of mammals. 



The neurites of the ventral roots are purely efiferent. Of these there 

 are two kinds, somatic motor and visceral motor. The somatic innervate 

 skeletal muscles derived from the mesodermal somites, the visceral are 



Docsal Root 



Venirat Roai 



Ramus 



dor^alis 



Fig. 330. — Diagram of the nerve components of a spinal nerve. Somatic motor 

 fibers are indicated by continuous lines; visceral motor in long broken lines; somatic 

 sensory in short broken lines; visceral sensoi»y by fine dotted lines. (From B. Patten, 

 after Froriep.) 



connected through the sympathetic ganglia with visceral involuntary 

 muscles or with glands. The ganglion cells of both types lie within the 

 gray matter of the spinal cord; but those of the somatic motor nerves 

 lie in the ventral column, while the visceral motor fibers come from 

 ganglion cells in the intermedio-lateral column. See Fig. 330. 



