The Development of the Mammalian Pituitary Body 



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the wall of the cerebral vesicle. No doubt this process is contributory to 

 the formation of Rathke's pouch and infundibulum, but it is probably of 

 morphological significance as well, and betokens the existence in an ancestral 

 vertebrate of a communication between buccal cavity and neural canal. 



A later stage of development is shown in fig. 3, which is taken from a pig 

 embryo of 12 mm. The buccal mucous membrane is now widely separated 



Fig. 3.— jMesial sagittal section through part of head of a 12-mm. pig embryo. 



a, Rathke's pouch ; b, beginning of infundibular process ; c, blood-channel ; d, remnant of Seessel's 



pouoh (V) ; e, notochord. 



from the wall of the cerebral vesicle, except at that part where the 

 anterior wall of Rathke's pouch closely adheres to it. The infundibulum 

 is only beginning to form, and the cells lining the cerebral vesicle at this 

 point have proliferated and elongated, and look more like ependjana 

 cells. There is no indication of any proliferation of cells of the fore-gut. 

 Rathke's pouch is median in situation, its neck is constricted, and serial 

 sections show that there is no lateral origin of the pituitary. The note- 

 chord persists, but has no immediate relation to Rathke's poucli. It takes 



