THE FROG AND ITS RELATIVES 257 



position it is able to avoid observation, and so escapes from large 

 water birds which feed upon them. 



The ears are located just behind the eyes and consist, externally, 

 of the round tympanic membrane, which is connected with the 

 internal ear beneath and also with the mouth cavity, by means of 

 the eustachian tube. 



Legs. The anterior legs are short and weak. They are provided 

 with four inturned toes, which help little in locomotion but serve 

 as supports to the body when on land. The hind legs, however, 

 are enormously developed and adapted in several ways for leaping 

 and swimming. The thigh and calf muscles are very powerful 

 and are so attached to the hips that they move the legs as very 

 efficient levers, in locomotion. Added to this is the great develop- 

 ment of the ankle region and toes, which together are longer than 

 the lower leg and add greatly to the leverage of these organs. Be- 

 tween the five long toes is developed a broad flexible web membrane, 

 which accounts for the frog's notable ability as a swimmer. 



Some frogs can leap fifty times their own length or twenty times 

 their height, while a man, to equal this feat would have to make a 

 broad jump of three hundred feet or clear the bar at a height of 

 one hundred and twenty feet. 



The legs of the frog are homologous to the paired fins of the 

 fish but resemble much more closely our own arms and legs. A 

 study of a prepared skeleton of the frog shows that the foreleg 

 has the same regions as our arm. The hind leg even more closely 

 resembles our leg, though with many differences due to being 

 adapted for very different functions. Still the homology is plain 

 as the following table shows. 



