xiii.] THE FROG. 173 



The general disposition of the parts which are seen in 

 the mouth has already been described. 



Teeth are found attached only to the premaxillae, max- 

 illae and vomers. They are small, with recurved and 

 pointed crowns. New teeth are constantly being developed 

 in the gum to replace those which are worn out or broken 

 away. And as they attain their full size these teeth be- 

 come ankylosed to processes of the subjacent bone. 



The gullet passes without change of diameter into the 

 stomach, which lies on the left side of the abdominal cavity 

 and is nearly as long as it. The stomach narrows poste- 

 riorly and the almost tubular pyloric portion bends round 

 sharply and passes into the duodenum. A slight constric- 

 tion marks the pylorus. The duodenum runs forwards 

 parallel with the stomach, so that with the latter it forms a 

 sort of loop. At its anterior end it passes into the rest of 

 the small intestine (ileum), which is coiled up into a sort of 

 packet and lies on the right side of the abdominal cavity, 

 being held in its place by a mesenteric fold of the perito- 

 neum. From the comparatively narrow neck of the packet, 

 the small intestine proceeds backwards in the middle line 

 and opens into the anterior end of the dilated large intes- 

 tine or colon and rectum. 



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. 

 Much more delicate continuations of these folds are conti- 

 nued into the small intestine and are there joined by trans- 

 verse folds. 



The opening of the ileum into the colon is valvular, its 

 edges projecting backwards into the cavity of the colon. 

 On the dorsal aspect, this presents a slight forward dilata- 

 tion, which may be regarded as a rudiment of a ccecum. 



