CEREBELLUM 529 



Where the pons becomes the brachium pontis the large 

 trigeminal nerve will be seen entering its ventral surface, 

 nearer its upper than its lower border. 



With the exception of the restiform bodies, the whole of the 

 medulla oblongata enters the lower aspect of the pons, and its 

 constituent parts are carried upwards within it. The pedunculi 

 cerebri emerge from its upper aspect. The dorsal surface of 

 the pons cannot be studied at present. It is turned towards 

 the cerebellum, which hides it from view, and it forms the upper 

 part of the anterior boundary or floor of the fourth ventricle. 



Cerebellum. The cerebellum is distinguished by the 

 numerous parallel and more or less curved sulci which 

 traverse its surface and give it a foliated appearance. As in 

 the case of the cerebral hemispheres, the grey matter is 

 spread over the entire surface, whilst the white matter forms 

 a central core in the interior. 



The cerebellum consists of a median portion, the vermis, 

 and two lateral hemispheres. The distinction between these 

 main subdivisions of the organ is not very evident on its 

 superior surface. Anteriorly and posteriorly there is a 

 marked deficiency or notch in the median plane (Fig. 223). 

 The posterior notch is smaller and narrower than the anterior 

 notch. It is bounded laterally by the posterior parts of the 

 cerebellar hemispheres, and anteriorly by the vermis, and 

 it is occupied by the falx cerebelli. The anterior notch is 

 much wider and, when viewed from above, it is seen to be 

 occupied by the inferior pair of quadrigeminal bodies and 

 the brachia conjunctiva cerebelli. Its sides are formed by 

 the lateral hemispheres, and the posterior end is bounded by 

 the vermis. 



On the superior surface of the cerebellum there is little 

 distinction to be noted between the vermis and the upper 

 surface of each lateral hemisphere. The upper surface of 

 the vermis forms a median elevation, from which the surface 

 slopes gradually downwards, on each side, to the margin 

 of the hemisphere. On the upper surface of the vermis four 

 regions are recognised. Anteriorly, at the posterior end of 

 the anterior notch, lies the central lobe, and prolonged up- 

 wards from it on the dorsal surface of the anterior medullary 

 velum, between the brachia conjunctiva, are a few folia which 

 constitute the lingula. Posterior to the central lobe is the 

 monticulus, separable into two parts an anterior elevated end, 



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