502 



ENCEPHALON. 



B— THE EITCEPHALOH. 



The encephalon admits of being conveniently divided into the 

 medulla oblongata, the cerebellum with the pons Varolii, and the 

 cerebrum. 



The medulla ohlongala is the part continuous with the spinal cord : 

 it rests on the basilar process of the occipital bone, and on its superior 

 or dorsal surface presents a groove continuous with the central canal of 

 the spinal cord. 



The cerelellum occupies the posterior fossa of the cranium. By the 

 mesial part of its anterior and inferior surface, it forms the roof of a 

 space, the floor of which is the grooved posterior surface of the medulla 

 oblongata, and which is named the fourth ventricle of the brain. On 

 each side of this, the cerebellum is connected with the medulla ob- 

 longata and cerebrum, and also receives the fibres of the ^wns Varolii, 

 which is a commissure, uniting the two hemispheres of the cerebellum, 

 and passing beneath and between the fibres which extend upwards 

 from the medulla oblongata. 



The cerebrum includes all the remaining and much the largest part 

 of the encephalon. It is united with the parts below by a compara- 

 tively narrow and constricted portion or isthmus, part of which, forming 



Fis. 353. 



Fig. 353. — Plan in outline of the Encephalon, as seen fkom the eight side. ^ 



The parts are represented as separated from one another somewhat more than natural 

 so as CO show their connections. A, cerebrum ; c, fissure of Sylvius ; B, cerebellum ; 

 C, pons Varolii ; D, medulla oblongata ; a, peduncles of the cerebrum ; b, c, d, superior, 

 middle, and inferior peduncles of the cerebuUum ; the parts marked a, b, c, C, form the 

 isthmus encephali. 



