70 



HUMAN PHYSIOLOGY. 



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 to consist of 

 fine fibrillse embedded in a clear, protoplasmic substance. Shafer 

 advocates the view that the fibrillae are exceedingly fine tubes filled 



Dendrites. 



Nerve-cell. 



Nerve process 

 or axon. 



Neurilemma 



Medulla, 



Neurilemma. 



Nerve-cell. 



FIG. 7. 

 A. Efferent neuron. B. Afferent neuron. 



with fluid. The axon varies in length from a few millimeters to 

 100 cm. In the former instance the axon, at a short distance from 

 its origin, divides into a number of branches, which form an intri- 

 cate feltwork in the neighborhood of the cell. In the latter instance 

 the axon continues for an indefinite distance as an individual struc- 



