144 PHILOSOPHY OF ZOOLOGY. 



a transverse hard and white membrane termed Corpus callo- 

 sum 9 appears, of considerable thickness, convex, with its an- 

 terior and posterior extremities incurved. At each of these 

 extremities^ the hemispheres are united by a medullary cord, 

 termed the anterior and posterior commissures. Under- 

 neath the corpus callosum, is the less dense partition, term- 

 ed Septum lucidum, the inferior arched side of which is 

 termed the Fornix. On each side of this division, the sub- 

 stance of the brain admits readily of a separation, exhibit- 

 ing two cavities, termed the Lateral Ventricles of the brain, 

 which are said to communicate with each other, near the 

 middle of the fornix. In the lower and interior parts of 

 each ventricle, there is a curved medullary prolongation, 

 termed Cornu Ammonls. In the anterior part of each ven- 

 triclej there is a pyriform eminence, of a cineritious colour, 

 and striated when divided. These are termed Corpora 

 striata. Behind these, lie two other eminences^ of a whiter 

 colour, united by a soft transverse plate of medullary mat- 

 ter, forming what are termed Thalami nervorum optlcorum. 

 Between these, there is another cavity* termed the Third 

 Ventricle of the brain < The communications between the 

 different ventricles^ and the fluids which they contain, are 

 still subjects of controversy. Immediately behind the tha- 

 lami, lies the Pineal Gland^ remarkable for containing small 

 concretions, like sand, consisting of phosphate of lime. Be- 

 neath this gland, are situated four medullary eminences, 

 termed Corpora quadrigemlna, the two superior and ante- 

 rior of which are called nates ; the inferior and posterior, 

 testes. In each lateral ventricle, there is a plexus of mi- 

 nute arteries and veins, which are expanded upon the op- 

 tic thalami, the pineal gland, and corpora quadrigemina. 



The CEREBELLUM occupies the inferior cavities of the 

 occipital bone, and is covered by the posterior lobes of the 

 cerebrum. Its surface is marked by transverse furrows, 



