{m) 



but that one of' them unites with the sulcus praepyramidalis ; in 

 other cases tliey grow along of each other, causing in this way an 

 asymmetry of the lobule, which influences the further lobulisation of 

 this region; these cases however are rather exceptional. The appea- 

 rance of these grooves is known in literature, and it is generally 

 believed that they form the sulcus horizontalis. In the beginning I 

 inclined to the same opinion, but the study of the abundant material 

 which was at my disposition instructed me that this notion is wrong, 

 and that this groove, Avhicli appears symmetrical!}', is the sulcus 

 superior posterior which separates the lobulus lunatus posterior and 

 the lobulus semilunaris superior. The sulcus horizontalis appears 

 afterwards in a manner as illustrated in Fig. 12 and 13. 



The fact that the sulcus superior posterior arises in an earlier period 

 of human embryonic life than the sulcus horizontalis seems of interest 

 in connection with other particulars of comparative anatomy. I found 

 namely in my researches on the cerebellum of Primates the sulcus 

 superior posterior appearing phylogenetically before the sulcus hori- 

 zontalis. All Primates excepted the Arctopitliecidae possess a sulcus 

 superior posterior, whereas a sulcus horizontalis is only to be found 

 in Anthropoids, although an indication is also to be found in Ateles. 

 After the formation of the sulcus superior posterior, the lobule between 

 the sulcus primarius and sulcus praepyramidalis quickly increases 

 in size, the cerebellum becoming convex in its median zone. (Fig. 11 

 and 12. 1, 4 and /)• 



In the same period in which the lobulus lunatus posterior - 

 bordered by the sulcus primarius and the sulcus superior posterior — 

 develops its secondary grooves, a short straight groove appears on 

 the upperlip of the sulcus praepyramidalis. This groove is the sulcus 

 horizontalis (Fig. 12 and 13,/<), which, contrary to the general concep- 

 tion appears in the median portion as an unpaii'ed groove. In the 

 beginning therefore the region between sulcus horizontalis and sulcus 

 praepyramidalis is extremely narrow in its median portion, the region 

 however between the first sulcus and the sulcus superior posterior 

 being relatively large. The tirst of these regions becomes the Tuber 

 vermis, while the second forms the Folium vermis. If one compares 

 the size of these regions with those of the Tuber and Folium vermis 

 of the adult cerebellum it is evident that there must be a very 

 unequal surface-expansion in these adjacent parts of the cerebellum 

 and that the development of this organ in man is not as simple as 

 it appears. And it may be concluded from the fact that the surface- 

 expansion of the lobules takes place with very different intensity that 

 the signification of the grooves and lobules is not merely a morpho- 



