STRUCTURE OF NERVOUS GANGLIA. 



221 



due to the pigment-granules of the cells, and partly to the redness of 

 the blood in the vessels, is wanting in the Invertebrata generally, and is 

 not characteristically seen in the classes of Fishes and Reptiles. More- 

 over, when the ganglionic substance exists in small amount, even in 



Fig. 70. 



Capillary network of Nervous Centres. 



Man, its colour is not sufficiently intense to serve to distinguish it ; and, 

 as we have already seen, there are nerve-fibres which possess a grayish 

 hue. The real distinction evidently lies in the form of the ultimate 

 structure, which is fibrous in the one case, and cellular or vesicular in 

 the other ; and these terms will be henceforth used to characterize the 

 two kinds of nervous tissue, which have been now described. 



380. A ganglion, then, essentially consists of a collection of nerve- 

 vesicles or ganglion-globules, interspersed among the nerve-fibres ; and 

 it is in the presence of the former that it differs from a plexus, which 

 it frequently resembles in the arrangement of the latter. When a 

 nerve enters a ganglion, its component fibres separate and pass through 

 the ganglion in different directions, so as to be variously distributed 

 among the branches which pass out of it (Fig. 71); coming, in their 



Fig. 71. 



Dorsal ganglion of Sympathetic nerve of Mouse ; a, 6, cords of connexion with adjacent sympathetic 

 ganglia; c, c, c, c, branches to the viscera and spinal nerve ; d, ganglionic globules or cells ; e, nervous t 

 crossing the ganglion. 



course, into relation with the vesicular matter, which occupies the inte- 

 rior of the ganglion, in one or more of the modes already specified 

 ( 3T8). Some of the fibres may terminate in the cells of the ganglion, 



