136 ELEMENTS OF HISTOLOGY. [Chap. xvi. 



Having entered the white matter, they take a longitu- 

 dinal direction. Most of these fibres enter the white 

 matter in the septa and septula, by which the nerve- 

 fibres of the white matter of the columns are sub- 

 divided, and ha,ving passed in a horizontal direction 

 in the septa and septula, some for a shorter, others 

 for a longer distance, they enter the columns and 

 pursue a longitudinal course. 



175. (3) The medullated nerve-fibres which leave 

 the cord by the anterior nerve roots are comparatively 

 thick fibres, which pass out of the anterior portion of 

 the grey matter of the anterior horns in bundles; 

 they pass through the white matter in an oblique 

 direction by septa, and emerge in the anterior lateral 

 fissure above mentioned. 



(4) The medullated nerve-fibres entering the cord 

 by the posterior nerve roots are thinner than those of 

 the anterior nerve roots ; they pass into the cord by 

 the posterior lateral fissure. Having entered, they 

 divide into two bundles, one median and another 

 lateral. The fibres of the former pass in an oblique 

 direction into the white matter of the posterior 

 columns the cuneiform fasciculus (see above) ; and, 

 having run in these in a longitudinal direction, again 

 leave them, sooner or later, and enter, in a horizontal 

 or slightly oblique direction, the grey matter of the 

 posterior horns. The fibres of the lateral bundle, 

 on the other hand, pass directly from the posterior 

 nerve root into the hindmost portion of the grey 

 matter of the posterior horn. The nerve-fibres of 

 the posterior roots entering the grey matter divide 

 repeatedly, and show very markedly the varicose 

 appearance. 



176. The g'ey matter consists, besides the 

 uniform network of neuroglia fibres and neuroglia 

 cells, of nerve-fibres and of nerve-cells, or ganglion cells. 



The nerve-fibres are of three kinds medullated 



