346 



THE FROG. PHYLUM CHORDATA 



EXTERNAL FEATURES 



In examining the body of a frog, we are struck, first by the fact 

 that its mottled green and yellow skin is soft and slimy and with- 

 out the covering of hairs, or scales, or feathers which we find in 

 other vertebrates, and next by its consisting only of head, 

 trunk, and two pairs of limbs. There is no neck or tail. The trunk 

 is flattened and bears the head at one end and the limbs of each 

 pair opposite to one another on the narrow sides. The eyes are 

 large, and have stout, almost immovable upper lids and thin, 



Fig. 260. — The Common Frog. 



translucent, movable lower lids which are different in structure 

 from those of man. The nostrils or external nares are a pair of 

 small openings on the top of the head in front of the eyes. Each 

 of them leads into a chamber which communicates with the 

 mouth. There is no flap to the ear, but the drum shows upon 

 the surface at the side of the head behind and somewhat below 

 the eye. If the drum be pierced, a bristle passed through it will 

 be found to reach the mouth. On the lower side of the trunk 

 there may be distinguished two regions — the large, soft-walled 

 belly or abdomen behind, and the smaller stout-walled breast 

 region in front. 



The two pairs of limbs correspond roughly in shape, each con- 



