THE ALDIEXTARY TEAl'T, Eli . 



I. THE ALIMENTARY TRACT. 



THE alimentary tract consists of the mouth or pharyngo-oral 

 cavity, the oesophagus, the stomach, the small intestine and the 

 large intestine ; these together forming a tube extending from the 

 mouth to the cloaca. From the commencement of the oesophagus, 

 at the entrance to the larynx, to the end of the cloaca, the length 

 of the tube is about 31-5 cm., that of the various parts being : 



From glottis to pylorus 5'5 cm. 



From pylorus to large intestine 2ro cm. 



Large intestine to end of cloaca 4 - o cm. 



Total length 31*5 cm. 



A. The Mouth. 



The mucous membrane covering the tongue will be described 

 with the sense-organs (see organ of taste). 



a. General description. The mouth of R. ezculenia, as in all 

 other amphibia, with the exception of the lowest (Siren, Proteus, 

 etc.), is of considerable width, and extends backwards as far as 

 the middle of the tympanic membrane. The upper margin of the 

 mouth possesses a lip or fold of the skin (SS 1 ). which projects suffi- 

 ciently to prevent the teeth being seen from the front or from the 

 sides. This lip-like rim is most prominent in the premaxillary and 

 superior maxillary regions, but can be traced along the whole length 

 <>f the upper jaw, and on to the lower jaw, by means of a well- 

 marked fold at the angle of the mouth. Beyond this point the lip 

 is absent, as the skin is closely attached to the bony mandible. 



On the roof of the mouth the following structures can be made 



T 2 



