220 



STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



them. In some instances, again, the ganglionic cell comes into relation 

 with the fibre, not by sending out a prolongation which is continuous 

 with it, but by being received into the cavity of the fibre (so to speak), 

 by an extension of the tubular wall over it. In other cases, moreover, 

 the fibres merely pass around and amongst the ganglionic cells, without 

 coming into direct connexion with them ; and when this is the case, the 

 ganglionic cells retain their simply globular character. Besides the 

 finely granular substance just, mentioned, these cells usually contain a 

 collection of pigment granules, which give them a reddish or yellowish- 

 brown colour : this, however, is frequently absent, especially among the 

 lower animals. The size of the vesicles is liable to great variation ; the 

 globular ones are usually between l-300th and l-1250th of an inch in 

 diameter. 



Primitive fibres and ganglionic globules of human brain, after Purkinje. A, ganglionic -globules lying 

 amongst varicose nerve-tubes, and blood-vessels, in substance of optic thalamus ; a, globule more enlarged; 

 b, small vascular trunk. B, B, globules with variously-formed peduncles, from dark portion of crus cerebri. 

 o50 Diam. 



379. The vesicles just described are aggregated together in masses of 

 variable size ; and are in some degree held together by the plexus of 

 blood-vessels (Fig. 70), in the midst of which they lie. They are sometimes 

 imbedded in a soft granular substance, which adheres closely to their 

 exterior and to their processes ; this is the case in the outer part of the 

 cortical substance of the human brain. In other instances, each cell is 

 enclosed in^ a distinct envelope, composed of smaller cells, closely adhe- 

 rent to each other and to the contained cell ; such an arrangement is 

 common in the smaller ganglia, and in the inner portion of the cortical' 

 substance of the brain. The substance which is made up of these pecu- 

 liar cells, of the plexus of the blood-vessels in which .they lie, and of the 

 granular matter that is disposed amongst them, is altogether commonly 

 known as the cineritious or gray substance ; being distinguished by its 

 colour, in Man and the higher animals at least, from the white substance 

 (composed of nerve-tubes) of which the trunks of the nerves, as well as 

 a large part of the brain and spinal cord, are made up. But this dis- 

 tinction is by no means constant ; for the gray colour, which is partly 



