(2) 



All the objects had been hardened in formol in .sita; alcoholic 

 material cannot be used for the study of this developmental process. 



A complete systematic investigation of the formation of the lobes 

 in the cerebellum of man has until now not been carried out. Retzius 

 giv^es in his well-known standard work — Das Menschenhirn — 

 a great number of pictures of developmental stages, also of the 

 cerebellum, but a reasoned explanation to them is lacking. Of an 

 earlier period we moreover mention the communications ofKöLLiKER 

 and ScHWALBE, of more recent date those of Kuithan, Elliot Smith 

 and Charnock Bradley. In general, however, these in\estigations 

 have been made with material which for this purpose was insufficient 

 and as a consequence of this, opinions have become current which 

 I have found to be wrong. This is more especially the case with the 

 view concerning the way in which the sulcus horizontalis develops. 

 Particularly with a view to the individual variations which arise 

 especially in the later period of the lobulisation, it is essential to 

 carry ont the investigation with an extensi\'e material, if we want 

 to form a clear and continuous idea of the process and if we desire 

 to distinguish well what is norm here and what exception. 



In the morphogenetic process of the iiuman cerebellum three 

 periods may be distinguished, the tirst period is that of the de\'elopment 

 of the "cerebellar lamella" until the appearance of the tirst cortical 

 groove ; the second and third periods are those of the formation of 

 grooves and lobes, during which, in the secoiid period, those grooves 

 appear which are generally characteristic for the cerebellum of mam- 

 mals, in the third, the specitic grooves and lobes of the Primate 

 cerebellum. In this first communication only the first and second 

 periods will be described. 



F'ig. 1, 2, 3 and 4 are suflicient to give an idea of the develop- 

 ment of the "cerebellar lamella" until the time of appearance of 

 the first groove. Fig. 1 has been taken from a foetus of 5 cm. 

 length from crown to sole. The cur\atures of the pons and neck 

 have reached their maximum. The cerebellum appears as the already 

 fairly thickened "cerebellar lamella" of Mihalcovics. It is remarkable 

 that the thickening is turned intraventricularly in man ^vhereas in 

 the rabbit and pig (Charnock Bradley) and tlie sheep (Kuithan) it 

 is exactly the extraventricular face which is most prominent. 



From figs. '2a and 3rt it appears that the convexity of the intra- 

 ventricular plane becomes greater and greater, while the outer plane 

 is only slightly vaulted. As a consequence of this, the cerebellum 

 has in Fig. 3 acquired a triangular shape in the section with one 

 extra- and two intraventricular planes; of these latter one faces 



