On a possible neural ridge origin of the adenohypophysis.

Serial sections of the hypothalamo-hypophyseal region in human embryos show the two hypophyseal primordia, beginning with the stage of four weeks. The emergence of the infundibulum is situated, at first, on the floor of the prosencephalon; Rathke's pouch appears as a vesicle without connection with any other structure. In the five-week embryo, Rathke's pouch fuses with the infundibulum and gives rise to a diverticular formation on the floor of the diencephalon. During the sixth week, the two connected primordia descend to the sphenoid cartilage and reach their final place. This fact, corroborated with the absence of any communication between Rathke's pouch and the stomodeum even in the stage of four and five weeks, and with numerous laboratory data that certify neural properties for the adenohypophyseal cells, drive us to the conclusion that Rathke's pouch has a neuroectodermal origin, in the neural ridges.