Sorensen, Study of Epiphysis and Roof of Dicncephalon. 1 6j 



water snake (Tropidonotus rhombifer) and shows the same 

 glandular structure and relations as were found in the black and 

 garter snakes. 



The glandular epiphysis of mammals is so well known and 

 has been so thoroughly studied that nothing need be said here 

 further than that its relation to the commissures and paraphysis 

 corresponds to that of the lower vertebrates. Three types have 

 been studied. Fig. 7, Plate XVIII, is a perpendicular section 

 of Erethizon dorsatus and shows a highly developed glandular 

 structure. Fig. 4, Plate XVIII, is a similar section of the 

 epiphysis and associated parts of the guinea pig. Fig. 6, 

 Plate XVIII, is a section of the epiphysis of an embryo mouse 

 and shows its primitive relation as an evagination of the roof of 

 the third ventricle immediately caudad of the supra-com- 

 missure. 



The Roof of the Diencephalon. It is evident from the 

 varied terminology met with in different writers, that a suffi- 

 ciently comprehensive study of the roof of the diencephalon 

 has not been made, to venture many generalizations pretending 

 to cover the variations found in the different groups. At pres- 

 ent about all that can be done is to call attention to the modifi- 

 cation found in different groups by the various investigators, 

 and suggest their probable bearing upon ones own personal re- 

 search. In our work upon the vertebrates we have found the 

 simplest relations to obtain. Three different structures, commis- 

 sures, epiphysis and paraphysis, have invariably been found, and 

 these always in the same relative positions, there being one nota- 

 ble exception, the alligator, where the epiphysis seems to be ab- 

 sent". Where modifications have been encountered they have 

 been those of the epiphysis and paraphysis, these taking differ- 

 ent forms in the same and in different groups. 



The Epiphysis. Beginning with the fishes and running 

 through the vertebrates we find the epiphysis to be a simple 

 evagination of the roof of the thalamus immediately caudad of 

 the supra-commissure. To this there is one exception, the 

 toad, where the epiphysis arises in front of the post-commis- 

 sure, there being a long segment of the roof between the supra- 



