Stroud, Mammalian Cerebellum. 9 1 



gions do constitute a single dilatation of brain tube, they are 

 separated, in the embryo at least, by a flexure which involves 

 the entire brain tube. ^ In their essential characters they are as 

 distinct from each other as is the myel from the cerebrum. 



Therefore it seems to me that the epencephal constitutes a 

 definitive segment of the brain, having a floor, roof and sides. 

 The cephalic walls and roof are convex ectad, and concave 

 entad. They may be compared to segments of a hollow sphere, 

 as the skin of an orange. They are the dorso-meso-caudal 

 extensions of the floor on each side whose meso-caudal borders 

 are divaricated, but still united by the thinner deckplate. These 

 semicircular plates are the Kleinhirnlamelle of Mihalkovics (22, 

 53). But it is not probable that anything more than a compar- 

 atively narrow strip of their caudal portions develops into the 

 cerebellum. Compare Figs, i, 4, 6, PI. I, and Figs. 24a, PI. 

 Ill, 42, PI. IV. 



It would appear that these caudal portions or protons are 

 the corpora restiformia of Tiedemann (31). 



The embryonic epencephal may be described as a segment 

 of the brain tube lying next caudad of the mesencephal. It 

 begins at the isthmus and ends at the pons flexure. Consid- 

 ered apart from the remainder of the brain it is a subcylindrical 

 tube whose cephalic boundary is contracted at the isthmus and 

 the caudal extremity is widened and rolls out something like 

 the bell of a brass horn, with this difference, the rim extends 

 only around the sides and roof The floor is continuous with 

 that of the metencephal, but is demarcated from it by the pons 

 flexure. 



At the isthmus, the tube is constricted to about one half 

 the diameter of the mesencephal ; it gradually widens caudad. 

 Thus there results a subcylindrical funnel-shaped tube composed 

 of substantial nervous substance, whose roof and sides are con- 

 tinuous with the metatela. 



The tela is joined to the substantial nervous substance 

 around its entire circumference ; between the substantial parietes 

 and the tela there is a thinner, transitional margin which grad- 

 ually merges into the tela. The term kilos is proposed to des- 



