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 

 l 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 Up, and on the 

 inner side is a groove, the 

 sulcus marginalise which re- 

 ceives the lower jaw when it 

 is closed. Anteriorly this 

 groove is crossed on each 

 side by a low elevation, the 

 pulviriar rostrate; immedi- 

 ately behind the tip of the 

 jaw the sulcus is deepened 

 again, forming the median 

 sub rostral fossa; on each 

 side of the pulvinars are the 



Fig. 8. — Mouth of the frog widely 

 opened. E, Eustachian tubes ; 

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

 eral subrostral fossa; M, median 

 subrostral fossa; A 7 , posterior 

 nares ; O, oesophagus ; P, pulvi- 

 nar rostrale ; S, opening of the 

 vocal sac ; T, tongue ; tp, tuber- 

 culum prelingnale. 



