372 PHYSIOLOGY 



middle lobe turned towards the fourth ventricle is known as the inferior 

 vermis, the dorsal surface forming the superior vermis. Each vermis and 

 each lateral lobe is subdivided into a number of smaller lobes. The intimate 

 structure of all parts of the cerebellum is however very uniform. It consists 

 of a mass of white matter internally, covered by a layer of grey matter, the 

 extent of grey matter being largely increased by the formation of numerous 

 parallel and more or less curved grooves or sulci which give the whole organ 

 a laminate appearance. In the mass of white matter, which forms the 



Extl. gen. body 

 Infr. brachium 

 Intl. gen. body 



Mesial Hil.-t 



Crusta 



Superior quadri- 

 geminal body 



Optic tract 



Fio. 188. Transverse section through human mid-brain at the level of the .superior 

 corpus quadrigeminum. (CUNNINGHAM.) 



core of each lateral hemisphere, is an isolated nucleus of grey matter known 

 as the corpus dentatum. In the white matter of the middle lobe is another 

 mass of grey matter known as the roof nucleus or nucleus fastigii. Be- 

 tween the nucleus fastigii and the nucleus dentatum are two other nuclei, 

 the nucleus globosus and the nucleus emboliformis. 



THE MID-BRAIN 



A little further forward the fourth ventricle comes to an end, and the 

 section passes through the mid-brain (Fig. 187), the cavity of the second 

 cerebral vesicle being represented by the narrow Sylvian aqueduct, bounded 

 dorsally by the corpora quadrigemina and ventrally by the crura, the stalks 

 of the brain. The crura are divided by an irregular mass of grey matter, the 

 substantia nigra, into two parts. The ventral portion is known as the. pes or 



