S70 



At an early stage in its developmental history two fissures 

 (floccular and parafloccular) cut into the lateral margin of the cere- 

 bellum and mark off a small caudal (ventral) appendage, which is the 

 flocculus, and a second, more anterior (dorsal) appendage, which 

 Stroud (2) has called "paraflocculus" (Fig. 2). 



Although these two bodies are formed independently the one of 

 the other they present so many features in common, which distinguish 

 them from the rest of the cerebellum, that they may conveniently be 

 grouped together as the lob us flocculi. 



The rest of the organ becomes subdivided at a very early period 

 (Fig. 4) by three fissures which begin in the vermis and extend in the 

 lateral direction. The deepest of these (in all adult brains) is the 

 fissura prima [fissura praeclivalis (auct.); sulcus primarius (Kuithan); 

 furcal sulcus (Stroud)], which forms the caudal boundary of the lobus 

 anticus and the cephalic boundary of the lobus medius. The caudal 

 limit of the latter is indicated by the fissura secunda [sulcus (vel 

 fissura) praepyramidalis (auct.)], which is the latest of the three 

 "vermian" furrows to make its appearance in development. The regiou 

 below (morphologically behind) the fissura secunda becomes split up 

 by the most precocious but shallowest of the three "vermian" fissures, 

 which is commonly called "postnodularis" (Fig. 3), into two parts — 

 uvula and nodulus. Although these two lobules become separated the 

 one from the other long before (see Fig. 3) the other lobes and lobules 

 become mapped out, they are so small and present so many features 

 in common that it is convenient to group them together as one lobe, 

 which I shall call "posticus". In the course of its development the 

 lobus anticus becomes subdivided (except in Notoryctes) by the 

 fissura praeculminata [even in many cases (e. g. , Dasyurus, 

 Sminthopsis, Trichosurus, inter alia) before the fissura secunda 

 makes its appearance (Fig. 4)]; and soon afterward the fissura post- 

 lingualis (commonly called "praecentralis") makes its appearance, so that 

 the anterior lobe becomes split up into three parts, the homologues 

 of which in the human brain are known as the lingula, lobulus cen- 

 tralis and culmen monticuli respectively from before backwards. 



In order to avoid the use of the term "centralis", I have called 

 these subdivisions respectively the pars lingualis, pars praeculminata, 

 and pars culminata of the anterior lobe. 



The only fissures crossing the mesial plane which are absolutely 

 constant in all mammals are those which I have called prima, secunda 

 and postnodularis. 



Soon after the fissura secunda makes its appearance the fissura 



