427 



also extends into the taenia, so that the taenia comprises all the 

 elements essential for the cerebellum. The nuclei of the matrix-layer 

 are still arranged radially in respect of the inner surface. Downward 

 along the taenia the matrix decreases gradually and finally vanishes. 

 Then the taenia is exclusively built up by a single stratum of cubic 

 epithelial cells. The nuclei of these cells stain very dark with haemato- 

 xyline, but the state of the preparation does not enable me to re- 

 cognize with certainty mitotic division in these cells. Next follows a 

 thickening of the epithelial layer, which is at several places in- 

 vaginated in the fourth ven- 

 tricle by capillary loops, form- 

 ing thus a true tela chorioidea. 



Now the question arises, 

 in what way the gap is filled 

 up between the taenia and the 

 cerebellum, because a short 

 time later the attachment of 

 the tela chorioidea is found at 

 the infero'posterior border of 

 the cerebellum. His and Bolk 

 believe that the taenia becomes 

 adherent to the cerebellum and 

 simply unites with it. In my 

 opinion this process is not so 

 simple, because the taenia is 

 not long enough to cover the 

 whole postero-inferior surface 

 of the cerebellum; moreover 

 the structure of the matrix at 

 the bottom of the slit does not 

 seem favourable to this view. 

 I think therefore that slit be- 

 tween the taenia and the cere- 

 bellum is gradually filled up 

 by the matrix, while the taenia 

 pari passu increases in length till the final attachment of the tela 

 chorioidea is reached i). 



Considered in this way the anomalous appearance of the process 

 disappears. What exists here is a disharmony in the development be- 



1) Henschen has shown that a disturbance in this process may 

 lead to epithelial cyst in the cerebellum. 





.ckoziddijou 



Fig. 7. Projection of the cerebellum 

 upon the median plane. 5/1. Semi-schematic 

 figure. The line of insertion of the taenia is 

 indicated by crosses ; the vertical lines show 

 the places of the sections reproduced in 

 Figure 1 — 4. 



