XIII.] THE FROG. 159 



tuting a rudimentary diaphragm; which, it will be observed, 

 is situated in front of the lungs, and not behind them, as in 

 the higher animals. 



Thus, in the trunk, on the ventral side of the vertebral 

 column, the body presents two cavities, one large posterior 

 pleuroperitoneal cavity, and one small, anterior to the fore- 

 going, the pericardial cavity, and neither of these communi- 

 cates directly with the exterior, though in the female there 

 is an indirect communication by the oviducts. 



On the ventral side of the head, the very wide mouth 

 opens into a spacious buccal cavity, the roof of which is hard 

 and firm, while the floor is soft and flexible;, except so far as 

 the middle of it is occupied by a broad, flat, for the most part 

 gristly plate, the body of the hyoid bone. Within the lips 

 the upper jaw is beset with numerous sharp small teeth, and 

 two clusters of similar teeth are to be seen in the fore part of 

 the roof of the mouth ; the latter, being attached to the bones 

 termed the vomers, are the vomerine teeth, while the former, 

 attached to the premaxillce and maxilla?, are maxillary teeth. 

 The lower jaw or mandible bears no teeth. 



At the sides of the clusters of vomerine teeth are the 

 apertures termed posterior nares, by which the nasal chambers 

 communicate with the mouth. At the sides of the back part 

 of the throat two wide passages, the Eustachian recesses, lead 

 into the tympanic cavities, which are closed externally by the 

 tympanic membranes. In the male Rana esculenta the small 

 apertures of the vocal sacs are seen on the inner side of each 

 ramus of the jaw, close to the angle of the gape and nearly 

 opposite the Eustachian recesses. In the middle of the back 

 of the throat is the opening of the oesophagus, closed by the 

 approximation of its sides except during deglutition, while in 

 the median line of the hinder part of its floor lies a longitu- 

 dinal slit, the glottis. A fleshy tongue, bifurcated and free 

 at its posterior end, is attached anteriorly to the middle part 



