CHAPTER VII. 



THE VISCERAL OR SPLANCHNIC DIVISION OF THE NERVOUS SYSTEM. 



Up to this point our discussion of nervous structures has been chiefly of 

 those neurons whose bodies are located in the brain and cord, or which 

 connect the brain or cord with striped muscle or the organs of external 

 sense. These neurons, taken together, are. properly said to constitute the 

 somatic division of the nervous system. Sometimes this somatic division 

 is designated as the cerebrospinal system; a designation which is per- 

 niciously misleading, since the cerebro-spinal system (if the term is to be 

 used at all), includes more than the somatic division; includes, in fact, 

 all nervous tissue except the cells of the ' local ' plexuses, described below. 

 Those neurons which supply afferent and efferent connections between 

 the brain and cord and the viscera — the smooth-muscle tissues of the blood 

 vessels, skin, alimentary canal, etc., and the glandular tissues — are collec- 

 tively designated as the visceral, splanchnic or autonomic division of 

 the nervous system. Frequently, the word ' division ' is dropped out and 

 the expressions 'splanchnic system' (or visceral or autonomic, etc.) and 

 ' somatic system ' are used. It is to be remembered, however, that the 

 somatic and the greater part of the splanchnic divisions are really parts 

 of the cerebro-spinal system. There is some confusion in the use of terms 

 referring to the splanchnic system, and even in the classification of the 

 parts of the total system. The terminology and classification herein are in 

 accordance with Starling, who is a good authority to follow in this matter. 

 The distinguishing peculiarity of the visceral system of nerves, from 

 the morphological point of view, is the fact that the connection between 

 the brain-stem or spinal cord and the structures supplied by the nerve- 

 fibers is a two-neuron connection. This is true at least of the efferent 

 neurons. As regards the afferent, information seems to be lacking. Com- 

 petent authorities agree that the afferent visceral neurons of the spinal 

 roots have their cell bodies in the spinal ganglia, as do the afferent somatic 

 neurons, but do not decide whether these neurons extend to the visceral 

 periphery or connect synaptically in the ganglia with a second set of 

 neurons, as do the efferent visceral neurons. The efferent neuron which 

 has one termination (and usually its cell body) in the cord (or in the 

 brain stem), has its other termination in a ganglion at a greater or less 



