68 ELEMENTS OF NERVOUS TISSUE. 



between the two lateral masses of nerve cells of 

 either side. The anterior process runs into the ante- 

 rior, and the posterior, into the posterior root, of each 

 spinal nerve; and finally, the processes given off 

 above and below become continuous with the longi- 

 tudinal fibres of the cord (PL XII. fig. V.). It 

 remains now to be proved, whether or no a similar 

 disposition exists in the mammalia and in man. 

 in the encepha. Th e facts ascertained in relation to the minute 



Ion. 



structure of the nervous tissue of the encephalon, are 

 still more incomplete. Here, as in the spinal marrow, 

 there is a white substance possessing very little vas- 

 cularity, and composed entirely of nerve fibres, and a 

 grey matter consisting of vesicular elements mingled 

 with nerve fibres, and very numerous blood-capil- 

 laries. Besides the multipolar or caudate cells, whose 

 processes anastomose with each other, and become 

 continuous with nerve fibres, there exist large num- 

 bers of nuclei and spherical cells especially in those 

 portions of the grey matter of the brain and cere- 

 bellum which lie nearest the surface (PL XIII. fig. 

 II.). What is the nature and uses of these nuclei ? 

 Are they germs of future nerve cells, or are they 

 only the analogues of the oval nuclei which we found 

 mingled with the connective fibres of the ganglia ? 

 These are questions which remain to be answered. 

 As for the arrangement of the nerve fibres of the 

 encephalon, it is probable that they run from one 

 mass of grey matter to another, serving as commis- 

 sures but this is not positively established.* 



* Refer on this subject to the admirable researches " On the Minute 

 Structure and Functions of the Spinal Cord," by J. L. C. Shroeder van der 



