466 ELEMENTARY PHYSIOLOGY 



round the nerve-fibres, and since they thus form a support 

 and a covering for the fibres^ the latter no longer need 

 their natural external covering ; or, in other words, the 

 nerve-fibres of the white matter possess no neurilemma. 



As in the white matter of the cord, so also in the grey 

 matter, neuroglia occupies the spaces between the septa 

 derived from the pia mater, and forms the supporting 

 basis for the nervous constituents of the grey matter. 

 The neuroglia is gathered into a specially well-marked 

 layer immediately surrounding the central canal of the 

 cord (Fig. 150, c.g.s.), and also, in a modified form, into a 



Fio. 147. — A Neitroolia-Cell from the White Matter of the Spinal 

 Coed. (Schafer.) 



The body and processes of the cell appear black, since they were 

 deeply stained in order to bring out their details. 



conspicuous somewhat transparent mass at the outer end 

 of the posterior horn of the grey matter, where it is 

 knowai as the substantia gelatinosa of Rolando. 

 (See Fig. 150, sg.). 



The most striking feature of the grey matter is the 

 presence in its neuroglia of nerve cells, many of which 

 are very large and conspicuous, while others are smaller, 

 but still very evident ; the presence of these cells and 

 of a closely interwoven network of non-medullated 

 nerve-fibres, together with the covipar/itive absence of 

 niedullated nerve-fibres, form the chief contrast between 

 the structure of the grey and the white matter of the 

 sj)inal cord. 



