CHAP, ii ] OF CELLS AND OF NERVOUS FIBRES. 



377 



The nervous cells continue always with one or more fibres. 

 They are thus called, according to the number of these fibrous 

 prolongations, unipolar, bipolar, multipolar. Cells called apolar, 

 without nervous prolongations, are long admitted : but their 



FIG. 67. 



Ganglionary multipolar cell of the spinal marrow of the ox, with a rounded nucleus and a 

 nucleole : a, cylinder axis ; b, prolongations of the cell finely striated and fibrillary. 

 Very greatly magnified. 



existence is very problematical. The nervous cells having a 

 greyish tint, which they owe to their contents, the regions of 

 the nervous centres when they are gathered together in great 

 number have the same colour. Thus is constituted the grey 

 nervous substance, which we find on the surface of the brain and 

 in the central part of the spinal marrow in the mammifers, and 

 so on. 



