( 3 ) 



basalwards, the other can dal wards. The oi'iginal caudal edge of the 

 "Lamina cerebellaris" has consequently been shoved upward together 

 with the insertion of the epithelial ventricular roof. Since in the 

 mean time the plica-cborioidea has been formed, the peculiar condition 

 has arisen, described by His for the human cerebellum, of which 

 KuiTHAN, however, denies the existence, since he could discover no 

 trace of it in the sheep, although a complete developmental series 

 was at his disposal. The anterior i)lait of the plica chorioidea, the 

 so-called lamina chorioidea, is now stretched parallel to the intra- 

 ventricular plane of the cerebellum wdiicli is turned biickw^ards and 

 this gives origin to a slit-shaped space between this plane and the 

 lamella mentioned. His described this in this way that the lamina 

 chorioidea partially encloses the cerebellum like a sac and how far 

 this is the case appears from fig. 36 where the cerebellum is seen 

 laterally. Now in fig. 4 nothing is found any longer of this condition, 

 the plica chorioidea is now inserted at the edge of the cerebellum 

 which now^ is turned to the back. Also in this respect I can confirm 

 the observations of His against those of Kuithan, that namely the 

 lamina chorioidea lays itself upon the intraventricular plane and 

 coalesces with this. Through this the latter has become an extra- 

 ventricular plane and the plica chorioidea has obtained a new 

 secondary line of insertion with the cerebellum. At the same time 

 the outer plane has in this way become convex, the inner plane 

 shows as a first indication of the "tent" in its posterior part a 

 shallow groove which is to be distinguished as Incisura fastigii. 

 The primitive line of insertion of the lamina chorioidea has to be 

 sought in fig. 4 at the top of the extraventricular plane, laterally it 

 lies more caudally, as follows from fig. Sb. This developmental stage 

 of the cerebellum in man seems, by the peculiar way in which it 

 thickens, to differ fundamentally from that of other mammals, where 

 the cerebellar lamella retains in the section a more flattened lenti- 

 cular shape. 



At first the thickened lamina cerebellaris has the shape of a semi- 

 ring, standing vertically on the anterior part of the longitudinal axis 

 of the rhombencephalon and laterally passing into the still smooth 

 regio pontis without a sharp border (fig. 2h). Soon the lateral parts 

 of the lamina cerebellaris show a fairly strong clublike swelling 

 (fig. Sfj) by which a clear demarcation between cerebral base and 

 cerebellum is formed. These lateral swellings remind us of the bilateral 

 origin of the cerebellum in lower vertebrates (observed e.g. by Schaper 

 in Teleosteans). Yet this lateral demarcation is onl}' temporary ; as 

 soon as the pons begins to difierentiate, it disappears again and arises 



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