I.] THE FROG. 15 



Teeth are present only in the upper jaw and roof of the 

 mouth. They are small, with recurved and pointed crowns. 

 New teeth are constantly being developed in the gum to 

 replace those whicli are worn out or broken away, and as 

 they attain their full size these teeth become ankylosed to 

 processes of the subjacent bone. Their distribution and 

 characters are such as to render mastication an impossibility; 

 they are prehensile and utilized as hooks by means of which 

 the animal as it were gets outside its prey. The eversible 

 tongue is utilized as a means of capture of smaller creatures, 

 chiefly insects. 



The gullet passes without change of diameter into the 

 stomach, which lies on the left side of the pleuroperitoneal 

 cavity and is nearly as long as it. The stomach narrows 

 posteriorly and the almost tubular terminal portion bends 

 round sharply and passes into the small intestine. A slight 

 constriction {pylorus) marks their point of junction. The 

 small intestine runs forwards parallel with the stomach, so 

 that with the latter it forms a sort of loop; it is continued 

 on coiled up into a sort of packet which lies to the right 

 side of the pleuroperitoneal cavity, being held in its place 

 by a mesenteric fold of the peritoneum. Thence the small 

 intestine proceeds backwards in the middle line and opens 

 into the anterior end of the dilated large intestine. 



The inner wall of the stomach is raised up into a number 

 of strong longitudinal folds which project into its cavity 

 and give it a stellate appearance in transverse section. 

 Similar but more delicate folds are met with in the small 

 intestine, the lining-membrane of which is produced into 

 parallel series of semi-lunar folds whose free edges project 

 backwards. 



The opening of the ileum into the large intestine is val- 

 vular, its edges projecting backwards into the cavity of the 



