The Hypophysis Cerebri. 307 



the mesoblastic cells of the mesoblastic axis, seems to be 

 invading the mesoblast. This is the processus infundibuli 



(P.I)- 

 The epiblastic cells of the coelice of the encephalon are not 



branched, are crowded closely together, and have taken a 



deeper stain than the mesoblastic cells. The epiblastic lining 



of the processus infundibuli is many cells in thickness, the 



cells are columnar, with large oval nuclei and with nucleoli. 



The epiblastic lining decreases as it approaches the lining of 



the stomodceum. At the very apex of the hypophysis cerebri, 



the two epiblastic layers of the middle cerebral vesicle and 



the stomodaeum come in close contact, no mesoblastic cells 



intervening. For some distance these two layers lie side 



by side. 



The second series of observations was made on sections 

 of an embrvo about seventeen millimeters in lenjrth. At this 

 stage a number of important changes have taken place; but, 

 as in the tive millimeter embryo, when compared to the 

 embrvo chick, the nervous system and sense organs are not 

 developed in proportion to the other organs. The cerebral 

 hemispheres are formed, the eyes in many respects resemble 

 those of a chick of the fourth day, the internal ears are well 

 developed, the nasal pits are mere invaginations of the epiblast, 

 somewhat like those of a chick of the third or fourth day. 



From figure 5 it will be seen that the ccelife of the encepha- 

 lon are continuous, one with another; and that the cceli^e of 

 the anterior cerebral vesicle is prolonged downward, forming 

 a long funnel-shaped cavity, the infundibulum (I). The apex 

 of the infundibulum comes in contact with a flask-shaped 

 bodv, the hypophysis cerebri (H. C). Resting upon the 

 base of the flask-shaped hypophysis cerebri is an irregular 

 elongated body, the processus infundibuh (P. I). 



Figure 6 is an enlarged view of the same section from 

 which figure 5 was taken. The hypophysis cerebri is here a 

 large flask, the walls being formed of epithelium of consider- 

 able thickness, which is continued as the neck of the flask 



