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 upper 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 



FIG. 8. -- Mouth of the frog widely p u l vinar rostr alt ; immedi- 

 opened. , Eustachian tubes; 



G, glottis; /, lower jaw; L, lat- ately behind the tip of the 



eral subrostral fossa ; M, median j aw the su l cus j s deepened 

 subrostral fossa; A 7 , posterior 



nares; o, oesophagus; P, pulvi- again, forming the median 



nar rostrale ; S, opening of the subrostral fossa ; Oil each 

 vocal sac ; T, tongue ; tp, tuber- 



culum prelinguale. side of the pulvmars are the 



o- 



T* 



