Sorensen, Study of Epiphysis and Roof of Diencephalon. 27 



ent in Proteus. Immediately behind this the whitish plates 

 connected with the ganglia diverge, leaving a slit-like, oval or 

 triangular space, in the center of which lies the proximal por- 

 tion of the pineal stalk or processus pinealis. Close behind this 

 a white or grayish streak represents the post-commissure. 

 Upon the floor of this segment is an oval space, bounded by a 

 whitish area which represents the recessus opticus, or proximal 

 portion of the primitive optic stalk, which recess in Necturus 

 and Proteus extends directly into the centre of the rudimentary 

 optic nerve. There is a striking similarity, which may be merely 

 superficial, between this area and that surrounding the proces- 

 sus pinealis. 



In his paper (<5^-'88) Osborn does not describe, but draws 

 the following relations in Rana mugiens and R. esculenta, Meno- 

 branchus, and Emys europaea ; first, post-commissure, then 

 pineal, supra-commissure, and plexus. In Rana the pineal 

 arises immediately in front of the post-commissure, a segment 

 of the roof intervening between the pineal and the supra-com- 

 missure. 



Richard Kraushaar, (^-'84) gives the embryological de 

 velopment of Mus musculus (white variety) and also a summary. 

 He says : The epiphysis is developed from the forward project- 

 ing cavity of the processus pinealis which is composed of cylin- 

 drical cells. Its distal end is closed, while its proximal commu- 

 nicates with the ventricle of the diencephalon. The upper 

 part of the wall of the processus which is thickened into a club- 

 like form produces diverticles with small openings, by the inter- 

 vention of the surrounding vascular connective tissue. At the 

 same time the diverticle of the epiphysis is very much reduced 

 and persists only in the lower part where the wall is very small 

 and consists of cylindrical cells. Meanwhile the diencephalon 

 under the epiphysis is drawn out to a funnel-shaped projection 

 which is connected to its cavity. The so-called stalk alone re- 

 tains the structure of the brain tissue. 



Ahlborn (/-'84) discusses the nature of the pineal gland 

 and concludes (1) from the correspondence between the optic 

 vesicle, and the origin of the epiphysis from an evagination of 



