Mervin T. Sndler 403 



shoe-shaped depression marks the position of the mandible. The thy- 

 reoglossal duct is quite a large conical elevation. From its unequal 

 sizes and characters in this series of models it seems to be a structure 

 subject to considerable variation in its development. The larynx here 

 is further developed and its cross-section is decidedly T-shaped. Just 

 where the larynx arises there is a proliferation or overgrowth of epithe- 

 lial cells. This is the beginning of a process which eventually closes 

 the whole larynx for a period of foetal life. 



N 



Fig. 8. Lateral view of the model of tbe uose and pharynx of embryo CXLIV. 

 Magnified 1.5 diameters. Hyp., hypophysis; N., nose; Oe., oesophagus; Sub. mx. gl., 

 rudiment of the submaxillary gland; Thym., thymus; Thyr. 1., lateral thyroid rudi- 

 ment; T. p., depression caused by the inferior turbinate process; Thyr. m., median 

 thyroid rudiment; Tr., trachea; V. P.^, first visceral pouch. 



Embryo CXLIV. 



This embryo has a neck-breach length of 12 mm. and a vertex-breach 

 of 14 mm. It is about 5^ weeks old. This model also includes the 

 mucous membrane except the large endothelial plug which has nearly 

 closed the larynx at its point of juncture mth the pharynx. The 

 closure is characteristic of this and later stages. In this embryo it is 



