50 Journal of Comparative Neurology. 



Two blood sinuses lie one on either side of the Epiphysis. 

 The one lying posteriorly being considerably larger. 



The plexus, as was noted by Mr. Ritter, is an exceedingly 

 complex and intricately folded mass. Its points of origin, how- 

 ever, are not uncertain, as it forms the roof of the diencephalon 

 cephalad of the supra-commissure. The plexus, as in other 

 reptiles, consists of two parts. The posterior part, at least, is 

 identical with Burckhardt's " Polster. " The caudal extremity 

 unites with the supra-commissure and the cephalic end with the 

 hippocampal commissure and projects laterally a short distance 

 into the lateral ventricles. 



The connective tissue is also present as Mr. Ritter describes 

 it. 



So far from agreeing with Ritter that "the epiphysial 

 vesicle is not a portion of the epiphysis" we have seen that it 

 alone, with its stalk, has any claim to this name. 



III. The Roof of the Diencephalon. 



By A. D. SORENSEN. 



Professor V. Kupffer, in his interesting discussion of the 

 roof the Diencephalon,^ calls attention to the fact that the posi- 

 tion of the pineal and associated supra-commissura is not the 

 same in amphibia as in other groups. 



He says: "The roof of the thalamencephalon or dien- 

 cephalon (Zwischenhirn) in the usual sense lies in front of the 

 superior commissure in Acipenser, while in the frog, accord- 

 ing to Professor Osborn's drawings, it lies behind that 

 commissue. In Acipenser the supra-commissure and post-com- 

 missure are closely approximated, while in the frog {fide 

 Osborn), they are widely separated. In Acipenser the pineal 

 lies immediately cephalad of the post-commissure as in Amni- 

 ates and particularly in man, in the frog there is an extensive 

 segment of the brain roof, separating the pineal from the post- 



^ Studien zur vergleichenden Entwicklungsgeschicte des Kopfes. Heft .1. 

 1893. 



