THE NERVOUS SYSTEM. 



563 



The gray matter of the spinal-cord consists of numerous groups of 

 nerve-cells, of a close meshwork of medullated fibres, most of which are 

 very fine and delicate, and of an extremely delicate network of axis- 

 cylinders. This latter fine plexus has been called "Gerlach's network." 

 Mingled with it and supporting it, is the meshwork of the neuroglia, 

 which is finer even, in its structure, than that of the nerve-tissue, so 

 that except under proper staining and illumination, it may appear 

 granular. This is especially developed around the central canal, which 

 is lined with columnar ciliated epithelium, the cells of which at their 

 outer end terminate in fine processes, which join the nenrogliar network 

 surrounding the canal, and form the substantia gelatinosa centralis. 



Fig. 35U. Different types of neuroglia cells. (After v. Gehuchten.) 6, Neuroglia cells of the 

 white substance, and c, of the gray substance of the cord of an embryo calt. 



Neuroglia was formerly thought to be mainly present in the tip of the 

 posterior cornu of gray matter, forming what is known as the substantia 

 gelatinosa lateralis of Eolando, through which the posterior nerve-roots 

 pass. This is now known to be composed of very small nerve-cells and 

 their processes. 



Groups of cells in gray matter. The multipolar cells are either scat- 

 tered singly or arranged in groups, of which the following are to be dis- 

 tinguished on either side certain of the groups being more or less 

 marked in all of the regions of the cord, viz., those (a) in the anterior 

 cornu, (b) those in the posterior cornu, and (c) intrinsic cells distributed 

 throughout the gray matter. 



(a) The cells in the anterior cornu are large and branching, and 



