STRUCT U BE OF NERVE-CENTRES. 



375 



FIG. 138. 



fanglion-corpuscle ; but this observation has not been con- 

 rmed. The physiological import of these bodies seems to be 

 still quite obscure. 



The central termination of nerve-fibres can be better con- 

 sidered after the account of the vesicular nerve-substance. 



The vesicular nervous substance contains, as its name implies, 

 vesicles or corpuscles, in addition to fibres ; and a structure, 

 thus composed of corpuscles and intercommunicating fibres, 

 usually constitutes a nerve-centre : the chief nerve-centres being 

 the gray matter of the brain and spinal cord, and the various 

 so-called ganglia. In the brain and spinal cord a fine stroma 

 of retiform tissue called the neuroglia extends throughout both 

 the fibrous and vesicular ner- 

 vous substance, and forms a sup- 

 porting and investing frame- 

 work for the whole. 



The nerve-corpuscles, which 

 give to the ganglia and to cer- 

 tain parts of the brain and spi- 

 nal cord the peculiar grayish or 

 reddish-gray aspect by which 

 these parts are characterized, 

 are large, nucleated cells, filled 

 with a finely granular material, 

 some of which is often dark like 

 pigment : the nucleus, which is 

 vesicular, contains a nucleolus 

 (Fig. 138). Besides varying much in shape, partly in conse- 

 quence of mutual pressure, they present such other varieties 

 as make it probable either that there are two different kinds, 

 or that, in the stages of their development, they pass through 

 very different forms. Some of them are small, generally 

 spherical or ovoid, and have a regular uninterrupted outline 

 (Fig. 138). These simple nerve-corpuscles are most numerous 

 in the sympathetic ganglia. Others, which are called caudate 

 or stellate nerve-corpuscles (Fig. 139), are larger, and have one, 

 two, or more long processes issuing from them, the cells being 

 called respectively unipolar, bipolar, or multipolar ; which pro- 

 cesses often divide and subdivide, and appear tubular, and filled 

 with the same kind of granular material that is contained 

 within the corpuscle. Of these processes some appear to taper 

 to a point and terminate at a greater or less distance from the 

 corpuscle ; some appear to anastomose with similar offsets 

 from other corpuscles ; while others are believed to become 

 continuous with nerve-fibres, the prolongation from the cell 



Nerve-corpuscles from a ganglion 

 (after Valentin). In one a second nu- 

 cleus is visible. In several the nu- 

 cleus contains one or two nucleoli. 



