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 re- 

 presents one of the above 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 

 everywhere, isolated and running in smaller or larger 

 bundles. 



178. The primitive nerve fibrillce form the greater 

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

 grey matter of all parts being composed, besides the 

 network of neuroglia fibrils, of an exceedingly fine 

 and dense network of primitive fibrillce (Gerlach). 

 These are the nervous 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 be- 

 come connected with this network of primitive 

 fibrillse. Numerous nerve-fibres take their origin in 

 the network of primitive fibrillae, and leave the grey 

 matter as medullated nerve-fibres, which pursue a 

 longitudinal course in the anterior and especially in 

 the lateral column of the white matter. 



179. The g-ataglion 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 

 relatively large nucleus bordered by a membrane, and 

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

 largest ganglion cells occur in the anterior horns, 

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

 the smallest in the posterior horns. The ganglion cells 



