513 



by a thick coating of very short cilia. The transition from the epi- 

 thelium which lines the grooves to that which lines the adjacent parts 

 of the brain-cavity takes place abruptly, and there are indications on 

 the latter of very much longer cilia than occur in the grooves. As far 

 back as 1873, indeed, Langerhans pointed out in his researches on 

 PetromyzoN, Planeri that the ventricles of the brain are lined with 

 ciliated cylinder- epithelium ^. 



The upper and inner part of each groove is in this region imbedded 



aPo Pooo o l"^^ ^r^^ &W 



^f^S'SnO Or, 



Fig. 2. Portion of similar section of the same specimen a short distance in front 

 of the last, showing the histological structure of the ciliated grooves. 



in the substance of the posterior commissure, the lower and outer 

 portion in the mass of cells which forms the inner part of the brain 

 substance (fig. 2). Anteriorly the two grooves diverge from one another 

 on the roof of the recessus sub-pinealis, and disappear in the deep 

 crevices between the ganglia habenulae and the side walls of the brain. 



2 Berichte über die Verhandlungen der Naturforschenden Gesellschaft zu 

 Freiburg i. B., Vol. 6. Heft 3. p. 8;i. 



34 



