The Frog: A Representative Vertebrate 53 



well-developed digits or fingers and a small rudimentary thumb. The 

 palm of the hand has various tubercles on it. During the breeding 

 season, the inner digit of the male has a thickened ridge, the nuptial pad, 

 which aids in clasping the female during copulation. 



The hind legs are long and powerful. Each consists of a thigh, 

 joreleg, ankle, and joot. The foot has five long slender toes connected 

 by thin webs which aid in swimming. 



MOUTH CAVITY 



When the broad upper and lower jaws are opened, the large 

 mouth or buccal cavity (Fig. 9) is visible. Posteriorly this cavity 

 narrows to form the pharynx. Near the anterior portion of the roof 

 of the mouth are the openings of the internal nares which are continu- 

 ous with the external nares and permit the passage of air into the 

 mouth. Just posterior to the nares are the large depressions into which 

 the eyeballs fit. Behind each eye and near the corner of the mouth are 

 the Eustachian tubes. Each tube passes to the corresponding middle 

 ear which opens behind the eardrum. These tubes function to equalize 

 air pressure on both sides of the drum. 



MAXILIX«r TKTH 



VOMERINE TEETH ,. . ,^~^ „ ^-^v^N .INTERNAL NAREl 



EYE SOCKET 



Fig. 9. — Mouth cavity of the male bullfrog. 



Between the internal nares and the eyes are two patches of teeth, 

 the vomerine teeth. Along the entire upper jaw are the fine conical, 

 maxillary teeth. Both these sets of teeth function only to hold food, 



not to chew it. 



On the floor of the mouth, the most conspicuous structure is the 

 tongue. This organ is flattened, rather fleshy, and attached at its 



