362 NERVOUS SYSTEM. 



are placed in layers, and are connected with the tubercula quad- 

 rigemina. 



The Corpora Striata, or the Ganglia Cerebri Antica, also two 

 in number, one for each side or hemisphere of the brain, are 

 situated before the thalami optici, at the bottom of the lateral 

 ventricles. They are about two and a half inches long, convex 

 on their upper surface, and e^ght lines broad at their front part, 

 but taper very gradually to a point behind. They are about 

 four lines apart in front, and are separated there by the septum 

 lucidum, but their posterior extremities diverge from each other, 

 so as to admit the thalami optici between them. 



The surface of the corpus striatum is cineritious, but within 

 it consists of cineritious and of medullary matter, placed in lay- 

 ers which alternate with each other. These layers are ar- 

 ranged in a crescentic manner, so as to present the convexity 

 upwards and the concavity downwards. The medullary sub- 

 stance is a continuation of that of the cruscerebri and of the optic 

 thalamus. It enters at the posterior inferior part of the corpus 

 striatum, and immediately divides into three layers, placed one 

 above the other, and of which the two inferior are more narrow 

 and short than the superior. The upper layer", in its progress 

 forwards, is interrupted by a body of cineritious substance, 

 which occasions it to divide into a multitude of distinct radi- 

 ated fibres. The same circumstance attends the olher layers, 

 but in a more limited degree. The medullary matter of the 

 corpus striatum may then be traced, in all directions, into the 

 hemisphere of the brain. The cineritious substance of the cor- 

 pus striatum is abundant, and is divided by some anatomists into 

 two kinds, one of a light gray, and another of a darker colour. 

 The first forms the middle and inferior part of the corpus stria- 

 tum: the second is in greater quantity, and is found principally 

 above and between the two upper layers. Such is the general 

 plan of the structure of the corpus striatum; but, it should also 

 be understood, that a close intertexture exists between its me- 

 dullary and cineritious matter. 



The most satisfactory way of exposing the structure of the 

 corpus striatum, is to scrape off its under surface, in tracing its 

 medullary matter from the crus of the brain, and through the 

 optic thalamus. It will then be seen, that the medullary sub- 



