THE STRUCTURE OF THE BRAIN STEM .17; 



to say that it consists of a middle and two lateral lobes. The surface of the 

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

 vermis, the dorsal surface forming the superior vermis. Each verm is 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 coi 

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



Inf. corpus quadrigeminum 



Grey matter 



Aqueduct of Sylvius 



^ Mesenc. root of 5th n. 



^Nucleus of 4th nrivr 

 brachium 



. long, bundle 



Raphe 



Supr. cer. peduncle 



Substantia nigra 



Crustu 



^ "^B^*^ 



FIG. 187. Transverse section through human mid-brain, on level of the inferior 

 corpora quadrigemina. (CUNNINGHAM.) 



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 

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

 as the corpw* dentatum. In the white matter of the middle lobe is anoth 

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

 tween the nucleus fastigii and the nucleus dentatum are two other 

 the nucleus globosus and the nucleus emboliformis. 



THE MID-BRAIN 



A little further forward the fourth ventricle comes to an end 

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

 cerebral vesicle being represented by the narrow Sylvian aqueduct 

 dorsally by the corpora quadrigemina and ventrally by the cnira, tl 



