410 E. A. BAUMGARTNER 
Several changes have taken place in the hypophysis of a 21 mm. 
embryo. It is still concave, both laterally and dorso-ventrally 
in its ventro-anterior surface (fig. 12). The thickened anterior 
wall of the hypophysis, reaching almost to the preoptic groove, 
is now distinctly evaginated. Scammon (’11) mentioned this 
closing off of the anterior part in a 20.6 mm. embryo and Sterzi 
(12) described the formation of this ‘rostral diverticulum’ 
in 20 to 24 mm. embryos. The lateral side of the anterior out- 
pouching is sharply demarcated by the formation of the stalk 
connecting the hypophysis to the mouth (fig. 19). The anterior 
endatthis stage is almost half as wide as the posterior, from which 
most of the hypophysis is developed. The opening from the 
mouth into the early anlage is located as before, but is smaller 
now. <A view of a model from the oral side shows that the con- 
striction of the front and lateral sides of the anterior end of the 
anterior lobe has begun. 
In a 22 mm. embryo the hypophysis (fig. 13) is not as concave 
as In younger stages. The anterior part shows laterally more 
marked constriction from the stalk which connects it to the buc- 
eal cavity. The anterior end is also markedly constricted. The 
opening into the hypophysis extends now from this anterior 
constriction to the posterior (caudal) margin of the opening into 
the first outpouching. The opening into the first evagination 
is very small and connects the pouch with the stalk (fig. 5). 
The posterior end is wider transversely than before. On its 
dorso-lateral surfaces are small ridges (fig. 13), the anlagen of 
the inferior sacs. On the ventral surface of the posterior part 
are two slight lateral furrows which are beginning to separate 
the inferior sacs from Rathke’s pouch (fig. 20). These furrows 
are present in a 20.6 mm. embryo, as Scammon (’11) stated. 
The lateral pouches or inferior sacs appear as dilated cavities 
at either side. The grooves or furrows are as yet shallow and 
indistinct. In an 18 mm. embryo, Scammon (11) noted 
the beginning of the division, by slight furrows, of the posterior 
portion into a median and two lateral parts. Some embryos do 
indicate the beginning division of the inferior sacs about that 
time but the furrows are not as prominent as the dilated cavities. 
