62 



HUMAN PHYSIOLOGY. 



branches, which then pursue opposite directions. (See Fig. 7.) The nerve- 

 cell maintains its own nutrition, and presides over that of the dendrites and 

 the axon as well. If the latter be separated in any part of its course from the 

 cell, it speedily degenerates and dies. 



AXOJfl 



NEVBILEMMA .... 



AXONE . 



A B 



FIG. 7. 



A. Efferent neuron. B. Afferent neuron. 



The axon, or nerve process, arises from a cone-shaped projection from the 

 surface of the cell, and is the first outgrowth from its protoplasm. At a short 

 distance from its origin it becomes markedly differentiated from the dendrites 

 which subsequently develop. It is characterized by a sharp, regular outline, 

 a uniform diameter, and a hyaline appearance. In structure, the axon appears 



