222 



THE NERVOUS SYSTEM 



comes the axis cylinder. Bipolar cells are prolonged in two 

 directions, and may be looked upon as simply protoplasmic 

 enlargements of the nerve fiber. This cell is frequently cov- 

 ered by a connective tissue envelope which is continuous in 

 both directions with the sheath of Schwann. Multipolar 



Dendrites. 



Nerve-cell. 



Nerve process, 

 or axone. 



Neurilemma. 



Neurilemma. 



Neive-cell. 



FIG. 65. 



A, efferent neuron; B, afferent neuron. (Brubaker.) 



cells have three or more prolongations, one of which always 

 becomes continuous with the axis cylinder and is called the 

 axis-cylinder process, the neuraxon, or the axone. The 

 other poles branch in various irregular directions like the 

 limbs of a tree, and are hence called dendrites. They also 

 go under the name of protoplasmic prolongations. Some of 

 these unite the cells to contiguous cells by interlacing with, 



