ANATOMICAL DESCRIPTION 



279 



--', Dendrites 



VCteH Body 



--------- Neuraxon 



....... Medulla 



\ ------ Node of Ranvier 



--- -Neurilemma 



divisions. The dendrons are thought by some to be con- 

 cerned only in absorbing nutriment for the nerve cell, 

 while other investigators believe them 

 to have also some part to play in the 

 conduction of nerve impulses. Each 

 neuron is anatomically independent 

 of every other. There is no continu- 

 ous path from one nerve cell to 

 another. The fine branches from 

 one cell mingle and interlace with 

 those of another cell, but do not 

 become connected with them to form 

 a continuous channel, any more than 

 do the interlacing branches of two 

 trees standing side by side form com- 

 municating channels for the passage 

 of the sap of one to the other. 

 Nervous influences do indeed pass 

 from one nerve unit to another by 

 some method not yet understood, 

 perhaps by a process similar to that 

 of electrical induction; but the old 

 idea of an uninterrupted channel for 

 the passage of a nervous impulse from center to periphery 

 and from periphery to center is now abandoned. There 

 may be several breaks in the course of transmission, as 

 there often are in the sending of a telegraphic message. 

 The two sorts of branches also preserve their identity 

 from beginning to end of each minutest filament. There 

 is no real network of nerve fibers in the nervous system. 



415. The Spinal Cord (Fig. 18, p. 28) is a column of 

 nervous matter from fifteen to eighteen inches in length 

 in the adult, from the foramen magnum, through which 



Nerve-ends 



Fig. 126. Diagram of a 

 neuron or nerve unit. 



