298 



LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



visceral components, the former dealing with structures in the body wall, the latter with those 

 situated in the viscera. The visceral impulses both motor and sensory are always transmitted 

 by way of the sympathetic system, except in the case of the visceral muscles of the gill region. 

 The spinal nerves transmit all four classes of impulses, while the cranial nerves are irregular 

 in this regard. The somatic sensory impulses arise in the sense organs peripherally located 

 in the body wall and pass along nerves whose cell bodies are nearly always situated in the 

 ganglia of the peripheral nervous system; the visceral sensory impulses arise in nerve endings 

 in the viscera; both pass into the central nervous system. The somatic motor impulses 

 arise from motor cells within the central nervous system and pass out in the nerves to the 

 voluntary muscles; the visceral motor impulses arise in the brain and cord, nearly always 



visceral sensory 

 nerve cell 



somatic sensory . 



nerve cells , SP™" 1 S">gl»on 



ventral column 



somatic motor 

 nerve cells 



communicating 

 ramus 



dorsal ramus 



somatic sensory fibers 



somatic motor fibers 

 ventral ramus 



epithelium of 

 digestive tract 



muscle layer 

 of digestive tract 



s visceral motor fiber 

 s visceral sensory fiber 



Fig. 68. — Diagram of a cross-section through the spinal cord and a spinal nerve to show the 

 functional components of the spinal nerve and their relation to the spinal cord and sympathetic system. 

 Somatic motor fibers, heavy continuous lines; visceral motor fibers, light continuous lines; somatic 

 sensory fibers, broken lines; visceral sensory fibers, dotted lines. (Slightly altered from Herrick's 

 Introduction to Neurology, courtesy of the \V. B. Saunders Company.) 



make a relay in the sympathetic ganglia or arise in those ganglia, and pass to the involun- 

 tary muscles, glands, etc. 68). (Fig. 



In addition to the foregoing, it will naturally be understood that a considerable part 

 of the central nervous system is concerned with the correlation and co-ordination of the 

 foregoing four classes of functions. 



4. The peripheral nervous system. — The spinal nerves will serve as examples, as they are 

 more typical. Each spinal nerve is connected with the spinal cord by two roots or bundles 

 of fibers, a dorsal and a ventral. The dorsal root bears a ganglion, the dorsal or spinal ganglion, 

 which consists of a collection of sensory nerve cells. The fibers springing from these cells 

 make up most of the dorsal root. This root enters the spinal cord and connects with the 

 dorsal gray column. The ventral root has no ganglion; its fibers arise from the somatic 

 motor cells of the ventral column and the visceral motor cells of the lateral column of the 

 gray matter of the spinal cord (Fig. 68). Beyond the ganglion both roots unite to form a 



