CEEEBELLUM. 475 



the posterior peduncles of the oerebellum The lateral walls of 

 the fourth ventricle are formed by the divergence of the xestiform 

 bodies. 



The superior pyramids are small bands of fibrous matter 

 between the superior mesian fissure and restiform bodies on each 

 side. They are a continuation of the superior columns of the 

 cord, passing to the crura of the cerebrum. 



The intermediate fasciculi are bundles of fibres, which pass 

 from the" lateral columns to the crura cerebri, between the resti- 

 form bodies and olivary fasciculi. 



PONS VAEOLII, 



The pons Varolii is the transverse projection on the base of the 

 brain, between the medulla oblongata and the crura of the cere- 

 brum ; it is lodged in the anterior depression on the basilar 

 process of the occipital bone, and has a groove for the basilar 

 artery along its middle line. It consists of a semicircular band 

 of white fibres, which stretch as a bridge from one side 'of the 

 cerebellum to the other, each extremity being curved upwards, to 

 form the thick processes, which constitute the middle peduncles 

 of the cerebellum. 



CEREBELLUM. 



The cerebellum, or lesser brain, is lodged in the posterior part 

 of the cranial cavity, immediately above the medulla oblongata, 

 and, in the domestic animals, behind the cerebrum, from which it 

 is separated by the tentorium cerebelli. It is globular or elliptical 

 in shape, the transverse diameter being the greater, and it consists 

 of a body and three pairs of peduncles, the anterior of which con- 

 nect it with the corpora quadrigemina, the middle with the pons 

 Varolii, and the posterior with the restiform bodies of the mod ilia 

 oblongata. 



The body of the cerebellum is composed of grey matter exter- 

 nally, and white in the centre. Its surface presents numerous 

 fissures, the two deepest of which run in a longitudinal manner, 

 so as to divide it into a middle and two lateral lobes. The middle 

 lobe projects beyond the lateral ones, and winds forwards, being 

 known as the vermiform process ; to its anterior extremity a thin 

 plate of white fibre, the valve of Vieussens, is attached, and 

 passes forwards to unite the anterior peduncles of the cerebellum. 



