406 Nose, Pharynx and its Derivatives in Man 



body witli a prominent horseslioe-shaped depression wliicli was very 

 noticeable in the model of embryo CXLIV. 



Embryo XXII. 



This embryo has a neck-breach length of 18 mm. and a vertex-breach 

 20 mm. It is an embryo of the 7th week. Seen from the side the 

 nose is joined to the pharynx further dorsally and is relatively de- 

 cidedly larger. The grooves representing the prominences of the jaws 

 are more distinct and the space between them shows as a prominent 

 flattened and slightly curved body (Fig. 10). The Eustachian tube is 

 more prominent and although still very much flattened has assumed 

 proportions nearer those of the adult. It is relatively more cephalic 

 than in the other models. The thyroid and thymus rudiments are 

 relatively further caudalwards. The epithelial plug of the larynx has 

 disappeared and left the opening free. The rudiment of the sub- 

 maxillary gland (Sub. max. gl., Fig. 10) is lobulated and more compli- 

 cated than in the model just described. Seen from above the main 

 body of the model is oval with the larger end ventralwards. The 

 Eustachian tubes project laterally and dorsally. Ventrally the nasal 

 cavities have approached one another and, instead of slanting away 

 from one another, tend to approach as they leave the main body of the 

 model. Seen from below the model shows a large rounded cavity for 

 the tongue with a notch in the ventral border for the frgenum'. All 

 traces of the thyreoglossal duct as a free opening has disappeared. 

 Taken as a whole, this model is decidedly more rounded and the 

 proportions are nearer those of the adult than in any of the embryos 

 studied. 



The Nose and Mouth. 



In His' " article on the formation of the nose he introduces the 

 subject by saying that the mouth and nose come originally from four 

 separate sources, viz. : — the two nasal pits, the stomodreum and the 

 pharynx (Kopfdarm). In regard to the nose he says the nasal pits 

 develop as separate pouches above the stomodseum and the story of 

 their development is the story of the development of the frontal process. 



In the model of embryo XII (a late two weeks' embryo) two of these 

 structures are present, the stomodaeum and pharynx, while the two 

 nasal pits have as yet not made their appearance. In an embryo of 

 the 4th week the stomoda?um and pharynx have united and the nose is 

 represented by two olfactory plates barely outlined in Fig. 3. 



" Loc. cit. 



