THE HYPOPHYSIS IN REPTILES 223 



In an Aromochelys embryo, 3.5 mm. long, there is a single, 

 median dorsal outpouching (Rathke's pouch) from the roof of 

 the mouth, which extends slightly forward toward the dien- 

 cephalon. The lateral walls of the pouch converge toward a 

 broad blunt apex which is about one-third as wide as the base. 

 The cranial surface is slightly concave and the dorsal surface 

 convex. The opening into Rathke's pouch is a wide horizontal 

 slit. 



In a 4.5 mm. embryo the anlagen of the lateral buds are well 

 marked. These are situated on either side of the hypophyseal 

 outpouching and are separated from the median portion by slight 

 furrows on the cranial side (fig. 60). A careful comparison with 

 plastic reconstructions of younger and older embryos shows 

 that these buds are not new outgrowths from the mouth, as 

 Gaupp believed them to be, but are constrictions from the sides 

 of Rathke's pouch. Although the notochord in this and later 

 stages is usually in direct contact with the caudal surface of 

 Rathke's pouch, in this specimen there is a projection on the 

 caudal side, near the base of the median part, to which the noto- 

 chord is applied (fig. 1). Whether this projection has any con- 

 nection with a constant growth from the caudal wall in older 

 embryos (to be described later) is uncertain. Because of the 

 constriction of the lateral buds, the base is about the same width 

 as the apex, the lateral walls extending perpendicularly to the 

 apex. The opening into the median hypophyseal outpouching 

 is about half as wide as it was in the earlier (3.5 mm.) stage. 

 Looking into this opening, as presented in the model, a deep 

 median lumen and two shallow lateral pockets may be seen. 

 The pockets are formed by the constriction of the lateral buds. 

 The three parts are continuous, however, and form the common 

 lumen of the hypophyseal anlage. 



In a 5.2 mm. embryo, the median portion or Rathke's pouch 

 is increased in length. The caudal surface is still concave and 

 the cranial surface convex. The apex is flattened dorso-ventrally, 

 and the lower portion, between the finger-like lateral lobes, is 

 constricted and circular in outline. The lumina of the lateral 

 lobes are relatively smaller than the median lumen, which is 



