728 THE NERVOUS SYSTEM. 



quite regularly and with a direction, somewhat curved, concavity forward, which 

 is outward and forward. On the lower surface the interlobular fissures have not 

 such a regular arrangement, but are much more curved, concavity forward, the 

 curves being greater in those placed anteriorly. 



The general outline of each surface has already been mentioned. 



UPPER SURFACE OF WORM AND HEMISPHERES. Each of these, as already 

 stated, is subdivided into lobules by the interlobular fissures. There are five 

 lobules and four fissures on the upper surfaces of the worm and hemispheres, 

 which, from before backward, are as follows (Fig. 425) : 



Lobules of superior worm : lingula, lobulus centralis, culmen, clivus, folium 

 cacuminis ; lobules of hemisphere (upper surface) : frcenulum, ala, anterior cres- 

 centic lobule, posterior crescentic lobule, postero-superior lobule. 



The interlobular fissures are the precentral, the post-central, the preclival, and 

 the post-clival. 



The complete arrangement is as follows : On each side of the lingula is the 

 frcenulum ; these three lobules are separated by the precentral fissure from the 

 lobulus centralis with its ala on each side. These three are in turn separated by 

 the post-central fissure from the eulmen, with the anterior crescentic lobule on each 

 side. Posteriorly to these is the preclival fissure, behind which are the clivus and 

 two posterior crescentic lobules, which are separated by the post-clival fissure from 

 the folium cacuminis and postero-superior lobules, and these last are limited below 

 by the great horizontal fissure. 



LOWER SURFACE OF WORM AND HEMISPHERES. The lobules of each of these 

 surfaces are four in number, separated by three fissures (Fig. 426). They are, 

 from behind forward, as follows : 



Lobules of inferior worm : tuber valvulce, pyramid, uvula, nodulus ; lobules of 

 hemisphere (lower surface) : postero-inferior lobule, digastric lobule, amygdala or 

 tonsil, flocculus. 



The interlobular fissures are the post-nodular, the prepyramidal, and the post- 

 pyramidal. 



The complete arrangement is as follows : The post-nodular fissure separates 

 the nodulus and the two flocculi in front from the uvula and two amyydalce 

 behind ; the prepyramidal fissure lies between the three last-mentioned lobules, 

 and the pyramid with a digastric lobule on each side, which in their turn are sepa- 

 rated by the post-pyramidal fissure from the tuber valvulce and postero-inferior 

 lobules, while between these last and the folium cacuminis and postero-superior 

 lobules of the upper surface runs the great horizontal fissure, which, in front, also 

 runs between the lingula and nodulus and their prolongations. 



LOBULES OF THE CEREBELLUM. As above mentioned, each group of three 

 lobules (central of the worm, lateral of the hemispheres) is limited either by two 

 interlobular fissures or by one such fissure and a portion of the great horizontal 

 fissure. Besides these there are other smaller fissures, known as intralobular, 

 which also run more or less transversely and cut up each lobule into still smaller 

 subdivisions or lamince, and which are quite irregularly disposed, especially in the 

 hemisphere lobules, where they may run obliquely, and, many of them, stop short 

 of the margin. Furthermore, the lobules vary greatly in size and, on the under 

 surface, in symmetry. 



The structure of each lobule (Fig. 428) is seen, on an antero-posterior section, 

 to consist of white matter surrounded by an irregular margin of gray matter, these 

 irregularities or indentations being due to the intralobular fissures ; while the 

 interlobular fissures are seen to be deep clefts separating the lobules. Hence the 

 cut surface of each lobule, whether of worm or hemisphere, looks like a dentated 

 leaf or folium, the branching stems of which are white matter, and the mar<jiii* 

 gray matter ; which last is also continued from lobule to lobule at the bottom of 

 each fissure (see also page 734). 



On the other hand, should the cerebellum be sliced from side to side, the plane 

 of each transverse section corresponding as nearly as possible to that of each inter- 



