XII.] THE TEETH. 421 



FIG. 141. 



DIAGRAM SHEWING THE DIVISION OF THE PRIMITIVE BUCCAL 

 CAVITY INTO THE RESPIRATORY SECTION ABOVE AND THE 

 TRUE MOUTH BELOW. (From Gegenbaur.) 



p. palatine plate of superior maxillary process; m. permanent 

 mouth; n. posterior part of nasal passage; e. internasal 

 septum. 



A palate grows inwards from each of the superior 

 maxillary processes (Fig. 141), which, meeting in the 

 middle line, form a horizontal septum dividing the front 

 part of the stomodaeum into a dorsal respiratory section, 

 containing the opening of the posterior nares, and a 

 ventral cavity forming the permanent mouth. These 

 two divisions open into a common cavity behind. This 

 septum on the development within it of an osseous 

 plate constitutes the hard palate. A posterior pro- 

 longation in which no osseous plate is formed consti- 

 tutes the soft palate. An internasal septum (Fig. 141 e) 

 may more or less completely divide the dorsal cavity 

 into two canals, continuous respectively with the two 

 nasal cavities. 



The teeth are special products of the oral mucous 

 membrane. They are formed from two distinct organs, 

 viz. an epithelial cap and a connective tissue papilla, 



