68 



THE BIOLOGY OF THE FROG 



CHAP. 



CHAPTER IV 



PRELIMINARY ACCOUNT OF THE INTERNAL STRUCTURE 



Mouth Cavity. — If the mouth of the frog is held widely 

 open, the following parts will appear. In the roof of the 



mouth there is a pair of 

 rounded prominences caused 

 by the eyes, as has already 

 been mentioned. Around 

 the margin of the upper jaw 

 is a row of fine, sharp, closely 

 set teeth which are conical in 

 shape and curved inward 

 more or less at the tip. Ex- 

 ternal to the teeth is a fleshy 

 fold, or tipper lip, and on the 

 inner side is a groove, the 

 sulcus marginalis, which re- 

 ceives the lower jaw when it 

 is closed. Anteriorly this 

 groove is crossed on each 

 side by a low elevation, the 



immedi- 

 ately behind the tip of the 

 jaw the sulcus is deepened 

 again, forming the median 

 subrostral fossa; on each 

 side of the pulvinars are the 



FIG. 8. - Mouth of the frog widely puMnar rostrale ; 



opened, h. Eustachian tubes; 

 G, glottis; /, lower jaw; L, lat- 

 eral subrostral fossa ; M, median 

 subrostral fossa; A'', posterior 

 nares ; O, oesophagus ; P, pulvi- 

 nar rostrale ; S, opening of the 

 vocal sac ; T", tongue ; //, tuber- 

 culum prelinguale. 



