FUNCTIONAL DIVISIONS OF THE NERVOUS SYSTEM. IOI 



visceral afferent and efferent divisions (Fig. 45). With exceptions 

 to be noted in their proper places, the four kinds of activities are 

 called for in all segments of the body, and consequently each of 

 the functional divisions is represented in each segment of the 

 body and all the segments of a given division are serially homolo- 

 gous with one another. These longitudinal divisions of the nervous 

 system are therefore the most fundamental and important divisions 

 both structurally and functionally. The segmentation of the nervous 

 system is to be regarded as a segmentation of each of the functional 

 divisions. It is probable that the functional divisions of the 

 nervous system are more fundamental than the metamerism of 

 the body. 



One point of contrast should be noted between the two somatic 

 divisions on the one hand and the two visceral divisions on the 

 other. Although somatic afferent impulses may produce somatic 

 reflexes directly without sensation, very commonly sensations 

 are produced. When present the sensations are definitely local- 

 ized and the responses may be consciously directed. Visceral 

 afferent impulses, on the other hand, usually produce reflexes 

 without sensation. When present the sensations are vague, 

 general, poorly localized, and consciously directed visceral activities 

 are very exceptional if not abnormal. The somatic activities 

 are par excellence related to the conscious life. 



There is given here for reference a table of the four functional 

 divisions with the structures included in each. In addition to 

 the structures included in this outline there are certain brain 

 centers which with their fiber tracts serve functions of correlation 

 between the four primary divisions. These will be treated in 

 later chapters (Chap. XIV and following). 



A. Somatic sensory division. 



i. General cutaneous subdivision. Consists of: 

 free nerve endings in the skin, 

 general cutaneous system of components, 



dorsal tracts of the cord, spinal V tract in the medulla oblongata, 



together with their accompanying nuclei : the dorsal horn, nucleus 



funiculi, nucleus spinalis trigemini, acusticum and cerebellum, 



secondarv tracts and centers: internal and external arcuate fibers 



