214 



INNERVATION. 



[CHAP. vni. 



nexion of which with the other elements of the nervous tissue has 

 yet to be ascertained. It is most probable, however, that they either 

 serve to connect distant vesicles, or else that they become conti- 

 nuous with the axis cylinders of the tubular fibres. In the cerebro- 

 spinal centre, we have found the tissue in the vicinity of the caudate 

 vesicles freely traversed in all directions by numerous very delicate 

 filaments, which seem to be the ramifications of the caudate pro- 

 cesses. These often exhibit considerable tenacity and elasticity. 

 The situations from which we may obtain such caudate vesicles as 

 are best suited for examination, are the locus niger in the crus 

 cerebri, and the gray matter of the cerebellum and spinal cord. 



. A large caudate nerve-vesicle, with diverging and branching processes, some of which, b, 

 are seen 10 pass off into extremely minute filaments. These seem to bear a very close resem- 

 blance to the central part of a tubular fibre, c, which is prolonged some way beyond the broken 

 edge of its tubular membrane and white substance, d. At e, are some small nerve-vesicles, stel- 

 late in form, doubtless from numerous processes given off from them : /, several extremely 

 small nerve-tubes, some of which are varicose. This figure exhibits the great variety of size of 

 the vesicles and tubes, a, is from the posterior horn of the gray matter of the spinal marrow, 

 and is magnified only 120 diameters, while the vesicles and tubes at e, from the gray matter of 

 the lower end of the cord, are magnified 300 diameters, d, is also from the spinal marrow, and 

 is magnified 200 diameters. 



The nerve-vesicles do not lie in immediate contact with each 

 other. They are either imbedded in a soft, granular matrix, as 

 in the brain, or enveloped in a capsule of nucleated cells, as in 

 the ganglia (fig. 54, /, g). The intimate connexion of this gran- 

 ular sheath to the vesicle, and to its processes when they exist, 

 increases greatly the difficulty of examining them. It is not easy 

 to detach them from this investment. This is generally effected 

 by accident more than by skill in manipulation, and it is along the 

 broken margin of the piece under examination that we shall succeed 

 in detecting the most perfect vesicles. 



