DEVELOPMENT OF THE FACE. 19 



of the permanent buccal cavity (see Fig. 15 B). The tongue is 

 developed in the floor of the pharynx and the tonsils in the 

 pharyngeal wall, but the lips, teeth, and gums are formed in the 

 walls of the stomodaeum. In the 3rd week of foetal life the 

 oral plate breaks down and the stomodaeum then communicates 

 with the pharynx. 



The Origin of the Pituitary Body. — The lining epithelium 

 (epiblast) of the stomodaeum becomes pouched out against the 

 floor of the fore-brain and forms the buccal element of the 

 pituitary (Fig. 15^4 and Fig. 22, p. 30). A process from the 

 floor of the hinder part of the fore-brain (thalamencephalon) 

 meets it and forms the neural part of the pituitary. The buccal 

 evagination is sometimes called Eathke's pocket. With the 

 development of the base of the skull, the stalk of the buccal 

 evagination disappears. A canal may occasionally be seen 

 passing upwards between the basi- and pre-sphenoid, and opening 

 at the olivary eminence, marking the position occupied by the 

 pocket in the foetus (canalis cranio-pharyngeus, Fig. 3). Gaskell, 

 who regards the neural or cerebro- spinal canal as the homologue 

 of the invertebrate alimentary canal, homologises the pituitary 

 evagination of the buccal epiblast with the invertebrate mouth 

 and gullet. 



