138 ELEMENTS OF HISTOLOGY. [Chap. xvi. 



of them, especially the larger ones, are only the first 

 part of the medullated nerve-fibres, being the axis 

 cylinder process of a ganglion cell, which process, 

 after a shorter or longer course in the grey matter, 

 becomes ensheathed in a medullary sheath, and 

 forms one of the medullated fibres. But there are 

 also numerous fine axis cylinders, which are the 

 last outrunners of the nerve-fibres entering the grey 

 matter by the posterior roots. They are seen every- 

 where, isolated and running in smaller or larger 

 bundles. 



178. The primitive nerve Jibr illce form the greater 

 part of the grey matter ; in fact the matrix of the 

 grey matter of all parts is composed, besides the 

 network of neuroglia fibrils, of an exceedingly fine 

 and dense network of primitive fibrillce (Gerlach). 

 These are the groundwork into which pass, and from 

 which originate, nerve-fibres. The nerve-fibres which 

 are derived from the posterior roots having entered 

 the grey matter of the posterior horn undergo 

 repeated divisions, and ultimately become connected 

 with this network of primitive fibrillse. Numerous 

 nerve-fibres take their origin in the same net- 

 work, and leave the grey matter as medullated nerve- 

 fibres, which pursue a longitudinal course in the 

 anterior and still more in the lateral column of the 

 white matter. 



179. The ganglion cells (Fig. 86) of the grey 

 matter are of various sizes and shapes, the branched, 

 or stellate, or multipolar shape being predominant ; 

 some have a more or less spindle-shaped or bipolar 

 body, but each extremity may be richly branched. 

 Each has a large nucleus enclosed in a membrane, and 

 in it is a reticulum with one or two nucleoli. The 

 largest ganglion cells occur in the anterior horns, 

 likewise in Clarke's column of the dorsal region ; the 

 smallest in the posterior horns. The ganglion cells 



