410 



SPECIAL HISTOLOGY. 



in order, all of them, to enter the anterior and posterior, grey 

 laminse, where we shall again meet them. Their nerve-fibres 

 (in the posterior roots, about | measuring 0*004 — 0-008'", 

 and i 0001 2 — 0003'", in the anterior about § measuring from 

 0006 — 0-011'", and \ 0-0025— 0003"') present, as soon as 

 thev have entered the cord, all the characters of the central 

 fibres, the largest, at their commencement, measuring about 

 0-004— 0-006'" in the sensitive, up to 0*008'" in the motor 

 roots. They continue, however, distinctly and constantly de- 

 creasing in size, until ultimately, the former, when they enter 

 the grey substance, have a diameter of scarcely more than 

 0-0012 — 0-0028'", and the latter in like manner one of not 

 more than 0-004'" (or in some of 0006'"). 



In the grey substance, the nerve-cells and fibres deserve spe- 

 cial consideration. The former present very various forms, all, 

 however, corresponding in one respect, that they are invariably 

 furnished with processes or prolongations, and, for the most part, 



Fig. 142. 



with many such, which repeatedly 

 branching, ultimately terminate in 

 extremely fine, pale fibrils, like 

 the finest axis-fibres. I distin- 

 guish : — 1. The cells of the central 

 grey substance. These (fig. 142) 

 are 0*004 — 0-008'" in size, always 

 pale and finely granular, with mul- 

 tiple nuclei and branching pale 

 processes, constituting as it would 

 seem the principal bulk of the 

 central grey substance ; but in 

 which, dark, true nerve-fibres also 

 occur, although of nearly the finest 

 kind, which can scarcely be recog- 

 nised as such, and are indeed very 

 few in number, and quite isolated ; 

 besides these, there are a good 

 many extremely fine, pale fibrils, like the processes of the cells, 

 only more extended, and running in a transverse and lon- 

 gitudinal direction, of which nothing more can be said, as 



Fig. 142. Cells from the grey central nucleus of the cord in Man, x 350 rtiaui. 



