PARAPHYSIS AND PINEAL REGION IN REPTILIA 325 



its termination. The shape of the epiphysis has also materially 

 changed. Its upper end has become much enlarged, is somewhat 

 hammer-shaped and quite broad in the transverse diameter. It 

 is barely separated from the tip of the paraphysis by the highest 

 part of the roof of the diencephalon. The enlarged extremity 

 is hollow, with relatively thick walls but the cavity soon termi- 

 nates in a very narrow solid stalk which represents fully three- 

 fourths of its total length. The stalk is closely applied to the 

 posterior wall of the post velar arch and becomes more and more 

 attenuated as it approaches the brain roof. As the specimen was 

 somewhat torn at this point, I am unable to state with certainty 

 whether it is still attached between the two commissures. The 

 wall of the epiphysis is rather thick and consists of several layers 

 of cells with large round nuclei. The preservation of the speci- 

 men did not permit of making a drawing to show the character- 

 istics of the cells here or in the wall of the paraphysis. The 

 superior commissure is now a large rounded tract and is separated 

 by a slight interval only from the anterior wall of the post velar 

 arch lying about opposite its middle point. As regards its rela- 

 tion to the floor of the diencephalon it lies about over the optic 

 commissure as in the preceding stage or if anything a trifle farther 

 back. The increasing size of the hemispheres seems to have 

 counteracted the forward push of the mid brain and the upper 

 part of the diencephalon seems to be inclined relatively further 

 back than in the last stage. This observation was made, however, 

 on a specimen cut in the sagittal plane, which was not perfect 

 and this statement possibly is open to some doubt. Elliot 

 Smith's (88) aberrant commissure, A. C, is seen as a well rounded 

 fiber tract lying in the original velum transversum. The tract 

 probably forms a more prominent projection into the cavity, 

 but again this part of the specimen was slightly damaged and 

 the model here is not absolutely perfect. The choroid plexus 

 of the lateral ventricle forms a very striking tuft in the ven- 

 tricular cavity. From its origin in the roof of the telencepha- 

 lon, immediately in front of and lateral to the opening of the 

 paraphysis, the plexus extends in the form of a round band of 

 tissue through the foramen of Munro into the lateral ventricle. 



