232 



THE CAT. 



[CHAP. ix. 



of rounded prominences may be remarked. These are known as 

 the corpora qitadrigemina, and the hinder pair, called the testes, are 

 rather larger than the anterior pair, which are called the nates 

 (Fig. 127, m). The corpora quadrigemina are solid, and do not 

 contain any internal cavity. In front of the midst of the anterior 

 pair, is a solitary prominence named the pineal gland. 



Just in front of and external to the corpora quadrigemina, there 

 is on each side a small prominence, 

 called the corpus geniculatum. It is 

 sometimes called the internal corpus 

 geniculatum, because, in man, there is 

 a second, contiguous, but more ex- 

 ternally placed prominence, named the 

 external corpus geniculatum a structure 

 which in the cat is hardly to be dis- 

 tinguished. 



The cerebellum is attached to the rest 

 of the brain by three pairs of processes 

 or crura. The first of these are included 

 in the fold of brain substance just de- 

 scribed. For this fold is exceedingly 

 thin at the middle of its hinder part 

 called the valve of Vieussens so that 

 the two thicker portions which laterally 

 border the thin part, are reckoned as 

 a pair of crura and spoken of as the 

 process-its a ccrcbcllo ad testes, on 

 account of the parts they connect. The 

 second pair of crura of the cerebellum 

 are the two lateral continuations up into it of the two sides of the 

 pons Varolii, and these are much the largest crura, and form the 

 principal connexions of the cerebellum with the rest of the brain. 

 The third pair of crura are the inferior peduncles of the cerebellum, 

 or restiform bodies, which are the continuations upwards and for- 

 wards of the posterior and part of the lateral columns of the spinal 

 cord. They diverge as they advance. 



The cerebellum is darker than the cerebrum. Its greatest 

 diameter is transverse, and it consists of two lateral lobes and a 

 median portion, called the vermiform process. The numerous more 

 or less parallel grooves on its surface indicate so many folds of grey 

 substance enclosing white matter within. The central mass of the 

 cerebellum is composed of white matter, and lamellar processes of 

 the same substance proceed in all directions from that central mass 

 into the darker enveloping layer. The cerebellum lies in that fossa 

 of the cranial cavity which we have seen to be bounded in front by 

 the petrous parts of the temporal bones, and behind by the line of 

 attachment of the tentorium to the occipital and parietal bones. 



The medulla oblongata lies upon the basi-occipital. Its anterior 

 inferior surface is marked by a median groove, on. each side of 



Fig. 127. UPPER SURFACE OF 

 BRAIN OF CAT THE CEREBRAL 

 HEMISPHERES BEING WIDELY DI- 

 VARICATED, TO SHOW THE PARTS THEY 

 NATURALLY COVER. 



-MS. Nates. 



pn. Pineal gland. 



ts. Testes. 



Sv. Superior vermis of cerebellum. 



Cc. Corpus callosum. 



5. Fifth ventricle. 



Cs. Corpus striatum. 



Cg. Corpus genieulatnm. 



Th. The optic thalamus. 



