82 THE CEREBELLUM. 



five divisions (irrespective of the white matter of the lingula and nodule), viz., two 

 ascending (central lobe and cnlmen), a posterior group (clivus, folium cacuminis, 

 and tuber valvulse), and two descending (pyramid and uvula). 



2. Arbor vita at transition of tvorm into hemisphere (fig. 59 B). With the 

 general enlargement of the organ as the worm passes into the hemisphere the white 

 centre becomes greatly increased in amount. This affects all parts of it, but first 

 and most markedly the corpus trapezoides and the root of the branch into the 

 culmen, which is here a large square mass of white matter from which three distinct 

 branches pass towards the upper surface of the culmen, which is subdivided by two 

 deep fissures (anterior and posterior intraculminate) into as many parts. A short 

 branch also passes forwards from the corpus trapezoides into the ala lobuli centralis. 

 The lingula is still seen in this section, and the superior medullary velum is 

 becoming thickened by the fibres of the superior cerebellar peduncle. The 

 horizontal stem of the arbor vitas is also much thicker, and from it the branches 

 of the clivus pass upwards as two main stems, which go towards the surface, 

 bifurcating as they approach it ; there are concealed folia in the pre- and post- 

 clival fissures. The postclival fissure is now deep, as is also the great horizontal, 

 and between the two a lobe, fan-shaped in section (the postero-superior), is now 

 visible, having a distinct large bifid branch of the arbor vitse directed upwards and 

 backwards into it, each ramus dividing more than once before reaching the surface. 

 Between the great horizontal and the postpyramidal fissure a large branch passes 

 downwards and backwards, and gives off several well-marked rami from its lower 

 border, three or more reaching the surface. The branch into the pyramid is broader 

 at its root ; in fig. 59 B, the section passes outside the uvula, and has taken a slice 

 off the amygdala. 



3. In a sagittal section altogether beyond the vermis and just within the limit 

 of the hemisphere, what in the worm constitutes the horizontal stem of the arbor 

 vitae, has become greatly enlarged, and has now blended with the enlarged corpus 

 trapezoides to form the large central white mass of the hemisphere (fig. 59 C). 

 In this the nucleus dentatus is now seen, and appears as a thin irregularly triangular 

 wavy band of grey matter, with the blunt apex of the triangle directed posteriorly 

 towards the horizontal fissure and the open base looking forwards and receiving the 

 great mass of fibres of the superior cerebellar peduncle which now replaces the 

 superior medullary velum. Above the level of the horizontal fissure seven or eight 

 principal processes of the white centre extend into the lobes of the upper surface : 

 the most anterior is small, and passes forwards into the diminishing ala lobuli 

 centralis ; three enter the anterior crescentic lobe (in the section here figured they 

 still appear to come off from a common stalk) ; two or three, the posterior crescentic ; 

 and a large branch directed obliquely upwards and backwards passes into the 

 postero-superior or cacuminate lobe : between these principal branches are a few 

 rudimentary ones passing into concealed lamellse, of which there are groups at the 

 bottom of the pre- and postclival fissures. Besides the postcentral and the pre- and 

 postclival fissures, two other fissures divide the anterior crescentic lobe into three 

 parts, and other fissures divide the posterior crescentic. The cacuminate lobe is not 

 thus subdivided by complete fissures. 



Below the level of the great horizontal fissure six or seven main branches come 

 off from the white centre. Two of these pass into the inferior semilunar lobe ; 

 one, the posterior, being very large and bifid or trifid ; one passes into each division 

 of the lobus gracilis, one into the biventral lobe, and a broad anteriorly directed 

 branch into the amygdala. A seventh small offshoot, directed almost due forward, 

 belongs to the stalk of the flocculus. In sections still further outwards (fig. 59 D) 

 the conditions are much the same as here described, except that the ala lobuli 

 centralis, and the amygdaloid branch are no longer seen, and the branch into the 



