PONS 483 



dorsum sellas of the sphenoid bone, and the medial parts of 

 the posterior surfaces of the petrous portions of the temporal 

 bones. It presents a median groove which gradually widens 

 as it is traced upwards (Fig. 192). The groove lodges the 

 basilar artery, but is not caused by that vessel ; it is due to 

 the prominence produced, on each side, by the passage 

 downwards, through the pons, of the bundles of fibres which 

 form the pyramids of the medulla oblongata. Where the 

 pons becomes the brachium pontis the large trigeminal 

 nerve is attached to its ventral surface, nearer its upper than 

 its lower border. 



With the exception of the restiform bodies, which pass 

 backwards into the cerebellum, most of the constituent parts 

 of the medulla oblongata are continued into the pons. The 

 pedunculi cerebri emerge from the upper aspect of the pons. 



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 vernris, 

 and two hemispheres, but the distinction between those main 

 subdivisions of the organ is not very evident on its superior 

 surface. Anteriorly and posteriorly there is a marked de 

 ficiency or notch in the median plane (Fig. 197). The 

 posterior notch is smaller and narrower than the anterior 

 notch. It is bounded on each side 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 colliculi of the quadrigeminal lamina 

 and the brachia conjunctiva cerebelli. Its sides are formed 

 by the hemispheres, and the posterior end is bounded by the 

 vermis. 



On the superior surface of the cerebellum there are, as 

 already stated, no definite lines of demarcation between the 

 vermis and the upper surfaces of the hemispheres. The upper 



