Sorensen, Study of Epiphysis and Roof of Diencephalon. 163 



segment of the roof. Cephalad of the supra-commissure we 

 have apparently two distinct evaginations of the membranous 

 roof. Thus far we have found no special significance in this 

 two-fold evagination. To say that we have here two anterior 

 epiphyses and term them as such is utterly out of the question. 

 The roof, as noted by Rabl Ruckhard (p. 24), is entirely mem- 

 branous. Their position in front of the supra-commissure ar- 

 gues that they are modifications of the diencephalic roof to 

 form the paraph ysis, and we are satisfied with such an interpre- 

 tation. As to their peculiar form, with other like peculiarities 

 in the paraphysis of reptiles we have little to say, except that 

 they will need to be considered in connection with the mechanics 

 of embryological development and will be further considered 

 when we come to discuss the roof of the diencephalon. Figs. 

 I and 3 are transverse sections showing the membranous plexi- 

 form roof of the thalamus. Rabl-Riickhard alone, so far as we 

 know, has studied the roof of the diencephalon and says that 

 " it is limited posteriorly by the post-commissure and the elon- 

 gated round conarium." His next statement, that " the roof 

 of the third ventricle is entirely membranous," is significant, 

 and accords with his figure (Plate XIX, Fig. 7), which, though 

 supposed to be the conarium, resembles the paraphysial projec- 

 tion immediately cephalad of the supra-commissure in our draw- 

 ings. As the structure supposed to be the conarium by Rabl- 

 Riickhard is shown only in a transverse section it is uncertain 

 whether it takes its origin immediately cephalad or caudad of 

 the supra-commissure and hence we cannot believe that what he 

 saw was the epiphysis (conarium) in view of the relations 

 shown in our drawings. We shall await with interest further 

 discussions, pro or con, on the diencephalic roof of the alli- 

 gator. 



In all other reptiles studied the epiphysis was found to be 

 present and the diencephalic roof to differ from from that of 

 fishes and amphibians in that both epiphysis and paraphysis are 

 highly developed. 



In Sceloporus striatum (Fig. 5, Plate XVI) we find essen- 

 tially the same structures described by us as existing in Phry- 



