212 E. A. BAUMGARTNER 



fragilis the cellular mass connecting the premandibular somites 

 is attached, either to the tip of the hypophysis, or directly caudal 

 to it. Oppel was convinced of the difficulty of proving whether 

 the hypophysis arises from the ectoderm or from the entoderm. 



In 1893 Gaupp's much-quoted work on the development of 

 the hypophysis in reptiles appeared. This has been of great 

 interest because of his description of a tri-lobed hypophyseal 

 anlage. Wax reconstructions of the hypophyses of Anguis fra- 

 gilis and Lacerta agilis show the hypophysis developing from a 

 median Rathke's pouch. The two lateral buds present in 2.5 

 mm. embryos were considered separate structures. Later, the 

 thickened epithelium anterior to the median hypophyseal anlage 

 evaginates, forming a four-lobed structure with one anterior, 

 two lateral and a median or posterior lobe. The four lobes 

 open into a common antechamber, the latter three by a common 

 lumen. In late stages the lateral lobes lie embedded in the 

 coverings of the brain, completely separated from the remainder 

 of the hypophysis. The isolated masses, Gaupp believed, per- 

 sist in the adult. 



Valenti ('95), studying Lacerta agilis, Lacerta vivipara, and 

 Anguis fragilis, readily distinguished the low, clear-staining ento- 

 dermal cells and the taller ectodermal ones in the hypophysis. 

 These cells could be recognized even after the rupture of the 

 oropharyngeal membrane. Valenti believed that the part played 

 by the ectoderm in the formation of the hypophysis was sec- 

 ondary, and that the hypophysis itself was possibly the remains 

 of an early branchial pouch and comparable to the thymus and 

 thyreoid. 



In a Sphenodon embryo of 'Stage L,' about 30 somites, Dendy 

 ('99) observed an epithelial thickening which he recognized as 

 the pituitary anlage. In stage N the notochord curves down- 

 ward in front of the hypophyseal outpouching. 



In an article on rudimentary cranial appendages, Melchers 

 ('99) considered the development of the hypophysis in Platy- 

 dactylus facetanus as passing through three stages; in the first 

 the orohypophysis, or Rathke's pouch, approaches the brain; in 

 the second the orohypophysis loses connection with the mouth; 

 and in the last stage various bud-like processes appear. 



