THE FROG AND ITS RELATIVES 



255 



tongue. This is attached at the front of the lower jaw, is very 

 muscular, and has two sticky fingerlike projections at its tip. 

 This peculiar tongue can be flipped out of the mouth so quickly 



FftOG 



ffjorecnrf Pos/no* 



IM WAT fit 



FIG. 91. Frog. External Features. 



Fig. i. Mouth Structure. The mouth is shown as if opened quite flat. 

 There are no teeth on the lower jaw, as they would interfere with the tongue 

 when extended as in Fig. 2. The teeth on the roof of the mouth are just where 

 they will catch any insect which has been flipped into the mouth by the tips 

 of the tongue. 



The openings into the vocal sacs enable the frog to inflate his throat and, 

 with these hollows as a sounding board, make such loud calls in the mating 

 season. 



Notice that the food has to pass over the trachea to reach the gullet, so the 

 former is protected by a sort of lip-like valve. 



The curved enlargements by the eustachian tubes are caused by the down- 

 ward projection of the eyeballs. 



Figs. 2, 3, and 4, show stages in the operation of the frog's tongue, in catch- 

 ing insects. 



The tip is two lobed and sticky, the mouth enormous in width, and the 



