Stroud, Mammalian Cerebellum. 95 



sich ablosende und die sackartige Hiille welche das Kleinhirn 

 noch im Beginn des 3 Monats bessen ist spater spurlos ver- 

 schwunden." 



The writer fails to obtain any such idea from his own speci- 

 mens. 



Main Divisions of the Cerebellum. — The dorsal aspect of 

 comparatively late embryos presents one mesal and three pairs 

 of lateral regions, viz : 



1. The vermis, azygous. 



2. The pilea, paired. 



3. The paraflocculi, paired ; in the lower mammals, each 

 is divided into supraflocculus and mediflocculus. 



4. The flocculi, paired. 



Of these the vermis is the last to appear, as might be ex- 

 pected from the method of development. 



The Pilea. — The regions which form the pilea apparently 

 are the first to be formed. Compare Figs. 8, 10, 56, 58. In 

 the adult cat they form quite prominent masses but receive their 

 highest development in man, where they form the chief mass of 

 the entire cerebellum. 



Their development is briefly as follows: Beginning with 

 the stage shown in Figs. 8 and 9, there are two lateral sub-ovate 

 masses, joined at the meson by a thin plate of substantial par- 

 ietes ; compare with Figs. 2, 4, 6, 52 and 58. On the lateral 

 aspect there is a slight depression which evidently foreshadows 

 the division into pileum and paraflocculus. The successive 

 changes are more readily traced in the cat because the enormous 

 human pileum obscures adjacent parts. 



The first distinct demarcation is into pileum and parafloccu- 

 lus by the parafloccular sulcus. This shows clearly in Fig. ii. 

 At a later stage, shown in Figs. 12, 13, and best in 14, a new 

 sulcus has appeared which divides the pileum into two regions, 

 prepileum and postpileum. The postpileum is very small in 

 Fig. 13, but it rapidly increases till it fully equals, if it does not 

 exceed, the prepileum ; see Fig. 17. After this stage the pre- 

 pileum grows rapidly till in the adult it is very large and well 

 developed, while the postpileum appears quite insignificant (Fig. 



