490 journal of Comparative Neurology and Psychology. 



Practically the whole of the membraneous roof of the telenceph- 

 alon is involved in the two complex structures, the chorioid plexuses 

 which extend into the lateral ventricles and the paraphysis which 

 projects upward between the lateral lobes. The essential fact is 

 that the membraneous roof extends forward over the interv^entricular 

 foramina to meet the lamina terminalis. The roof of the telen- 

 cephalon near the middle line is membraneous for its whole length. 



The questions regarding the anterior end of the brain and the 

 boundary between diencephalon and telencephalon have been most 



Fig. 25. Amblystoma p., after closure oi: neuropore, model of the right 

 half of the head, viewed from the medial surface, x 25. 



carefully studied in embryos of Amblystoma punctatum. In these 

 embryos the entoderm, mesoderm and notochord present essentially 

 the same features and the same relations to the brain as in selachians. 

 In particular, the premandibular somites, the median undifferentiated 

 mass in which the notochord ends anteriorly, and the preoral ento- 

 derm have the same disposition as in selachians. The only difference 

 is that all the structures are more compact in amphibians and the 

 preoral entoderm is shorter. As Figs. 23, 24, 25 show, the preoral 

 entoderm fills the angle between the floor of the neural tube (neural 

 plate) and the ectoderm and there is a short prolongation of the 

 archenteric cavity into it in front of the site of the future mouth. 

 The neural plate is bounded by neural folds which meet in front 

 in the transverse terminal ridge. This terminal ridge marks the line 



