Johnston, Functional Divisions of Nervous System. 91 



the splanchnic divisions have to do with the internal, vague, 

 poorly localized, general sensations and with movements of the 

 viscera related to the processes of nutrition, respiration, etc. 

 So far as simple reflexes are concerned, it is probable that the 

 somatic and splanchnic divisions remain independent. When 

 stimuli received by either sensory division give rise, or seem to 

 give rise, to reflexes in the other motor division, there has been 

 an intervention of higher nerve centers or of stimuli from some 

 other sense organ, such as the eye. An example of the latter 

 is found in body movements for the purpose of catching food. 

 We pass now to the comparison of the several regions of 

 the central nervous system with reference to the four functional 

 divisions. In the trunk region there is found a relatively sim- 

 ple condition in which all four divisions are represented, as fol- 

 lows : 



somatic sensory : dorsal horn of the cord, sensory fibers 

 with general cutaneous distribution. 



splanchnic sensory : region of Clarke's column, sen- 

 sory fibers distributed to viscera by way of the dorsal 

 roots and the sympathetic. 



somatic motor : ventral horn, motor fibers supplying 

 body musculature. 



splanchnic motor : lateral horn, motor fibers to the vis- 

 cera. 

 Associated with these four grey columns in the cord are fiber 

 tracts which are not important, however, for the comparison 

 with the brain. On the other hand, the commissural and tract 

 cells, which give rise to the greater part of the longitudinal 

 tracts of the cord, are of great importance for this comparison, 

 as will appear below. 



As the cord passes into the medulla each of the columns 

 undergoes certain modifications due to the increase or reduction 

 of the peripheral organs belonging to the same division. The 

 somatic motor column gives rise to the nerve comonly known 

 as the hypoglossus, which innervates tongue and tongue-shoul- 

 der-girdle musculature. This nerve is only a remnant composed 

 of a variable number of ventral roots (3 to 8 in Gnathostomes) 



