An Analysis of the Juxta-Neural Epithelial Portion etc. 279 



proacliing each other across the median line and thus afford the in- 

 fundibular process [2S] an epithelial investment upon its ventral sur- 

 face. The cavity of the buccal sac is confined to the neck [25c], 

 body and caudal projections; it does not extend into the tuberai pro- 

 cesses in this stage. 



The neural elements now present some important modifications 

 in their form, for whereas prior to this period the buccal sac has 

 been in relation with the infundibulum, infundibular process [28] and 

 the middle segment of the floor of the third ventricle, the floor [27] 

 itself becomes so modified as to give rise to the eminentia saccularis. 

 The evidence of this change is seen on the ventral surface in a sharp 

 median protrusion of the floor of the diencephalon [27] immediately 

 caudad of the optic chiasm, and extending toward the infundibular 

 process. The protrusion is most marked just behind the chiasm. 

 This new prominence has also a considerable transverse expansion so 

 that it presents a keel and two lateral surfaces. The keel is in 

 relation with the median dorsal elevation of the buccal sac; the 

 lateral surfaces are coming into relation with the tuberai processes. 

 A view of the third ventricle shows that this cavity has become 

 expanded in its more ventral portions. A diverticulum extends ce- 

 phalad beneath the post-chiasmatic process; this has its surface ex- 

 pression in the sharp cephalic prominence of the eminentia saccularis 

 immediately behind the optic chiasm. The expansion of the cavity 

 also involves the transverse diameters so that the recessus tuberis 

 is now manifesting the tendencies which will ultimately determine a 

 ventral extension of the third ventricle whose plane is at right angles 

 to that of the main ventricular chamber. In this stage, therefore, 

 all of the elements of the hypophysis, both neural and epithelial, are 

 present and rapidly assuming their definitive relations. 



31 mm Cat Embryo No. 144 (plate XIV, fig. 21). 



This stage serves to emphasize the results of the tendencies 

 observed in the 25 mm embryo. Each tuberai process [30] has come 

 into actual contact with the corresponding lateral surface of the 

 eminentia saccularis and at the same time has forced the greater 

 part of the dorsal surface of the buccal sac further away from the 



