216 BULLETIN OF THE 



excavation being the continuation of the cavity of the third ventricle 

 into the epiphysis. The conical end, then, is distal, and rises somewhat 

 above the level of the cerebral hemispheres. The curved axis forms 

 very nearly a segment of the circumference of a circle, and is directed 

 upward and forward from its point of origin from the brain. Continu- 

 ing anteriorly from the apex of the cone is a string of connective tissue 

 (con't. tis.), which passes to the region of the parietal vesicle, and in the 

 distal portion of its course comes close in contact with the dura mater 

 of the brain. The axis of the cylinder, if we consider it as continued 

 to the anterior termination of this connective-tissue string, describes 

 very nearly a semicircumference. The most anterior point in the con- 

 nection of the epiphysis with the brain is at the junction of the cere- 

 brum with the optic thalamus, somewhat anterior and dorsal to the 

 superior commissure (com. su.). For a short distance above its connec- 

 tion with the brain in this anterior part, the epithelial nature of the 

 epiphysial wall is less distinct than at a higher level, where the wall 

 becomes thicker, and is composed of a single layer of more or less cuboid 

 nucleated cells, which stain readily in borax carmine or heematoxylin 

 (Plate III. Figs. 8, 9, eHh.). Also at this level the wall becomes thrown 

 into a highly complicated system of folds ; and it is this folded epithe- 

 lium, containing within its folds great quantities of blood corpuscles, 

 that forms a large bulk of the whole epiphysis (Figs. 8 and 9, eHh. 

 and cp. sng.). 



In the section represented in Figure 9 no connection exists between 

 the epithelium of the posterior portion of the epiphysis and the brain, 

 and it is doubtful if such connection exists here in any of the sections 

 of this specimen ; at any rate, if it does exist, it is exceedingly thin 

 and limited in extent. There is, however, an undoubted connection in 

 this region in P. coronata, which will be described later ; but even in 

 this latter species the posterior wall of the epiphysis is much less de- 

 veloped than the anterior wall. The exceedingly thin epithelium that 

 forms the posterior wall in P. Douglassii would, as is evident from its 

 position and from comparison with P. coronata (Plate IV. Figs. 11 and 12), 

 form a connection with the brain roof had not a separation taken place, 

 either artificially or as a result of degeneration. This wall is closely 

 applied to the anterior, concave side of the blood sinus to be presently 

 described, and at a considerable distance above the brain is continuous 

 with the anterior wall of the epiphysis. The space included by these 

 walls is the hopper-shaped excavation in the proximal end of the cyl- 

 inder already mentioned, — an extension of the cavity of the third 



