Metasoa Rana. 267 



as \ve shall afterwards see, are formed as outpushings from 

 the alimentary canal itself. The two chief glands of this 

 nature are the liver and pancreas. 



It will be necessary now to describe the course of 

 the alimentary canal and the structure of that organ and of 

 the glands which open into it. It will be convenient to 

 subdivide it into four regions, viz. the buccal cavity, the 

 oesophagus, the stomach, and the intestine and to describe 

 in connection with these several regions the glands which 

 are specially related to them. 



The buccal cavity. The mouth is proportionally of large 

 size, the gape being very wide. The upper jaw is fringed 

 with a row of small teeth, and additional patches of teeth 

 may be felt on the roof of the mouth behind the jaw-teeth. 

 These are known as maxillary, premaxillary, and vomerine 

 teeth respectively from the bones of the skull on which they 

 are supported (p. 301). The lower jaw bears no teeth, but 

 has attached immediately behind its most anterior portion 

 the tongue, a flat bilobed organ of large size, free behind 

 and capable during life of being everted with great rapidity. 

 The large bulgings due to the eyeballs may also be noted on 

 the roof of the mouth. 



Six openings may be easily made out on the walls of the 

 buccal cavity. Most noticeable of all of course is the wide 

 pharynx, or upper part of the oesophagus, and close to it 

 the small slit-like glottis, or aperture of the respiratory 

 system. Two other apertures are visible in the hinder 

 portion of the cavity. These are the eustachian tubes 

 leading into the ears. Lastly, in front and on the outer side 

 of the vomerine teeth are two small apertures, the posterior 

 nares, or inner nostrils. 



The entire buccal cavity is lined by a continuation of the 

 outside skin termed a mucous membrane, since it contains 

 many small glands whose function it is to secrete mucus 

 a sticky, more or less watery fluid mainly of service in 

 keeping the membrane moist and facilitating the act of 



