250 FROGS, TOADS, AND NEWTS [CH. VIII 



three and four times as long as the wrist and hand. Most 

 remarkable is the great development of the astragalus 

 and calcaneum, tarsal bones which in the great majority 

 of animals are short and compact : here they are lengthened 

 out to such an extent as to render it possible for a beginner 

 to mistake these bones for tibia and fibula. The toes are 

 also of very great length, especially the 4th ; the hallux, 

 or " big-toe," is decidedly the shortest, and at its base is 

 the vestige of yet another digit. The leg may be regarded 

 as composed of three levers folded, in the resting attitude, 

 on one another ; when a leap is taken the three levers are 

 straightened out so as to lie in virtually one and the same 

 straight line, the toes giving the final push off from the 

 ground. The hind leg is the main instrument in swim- 

 ming: the feet are webbed as far as the penultimate phalanx 

 of the 5th, 4th, and 3rd digit on its outer side : there is a 

 moderate web between the 3rd and 2nd, and between the 

 2nd and 1st digits. Thus the outer and upper portion of 

 the foot makes the stronger part of the stroke in swimming 

 a fact that is of no small importance in enabling the frog 

 to dive quickly below the surface on entering the water. 

 It must be borne in mind that the adult frog, except at 

 the breeding season, prefers to be on land near the water 

 rather than in the water itself. He hastily takes refuge 

 in the water when alarmed and vanishes beneath the 

 surface. It is therefore of vital importance that the web 

 of the hind foot should urge the body downward. The 

 front feet are not webbed, and take but little part in actual 

 swimming, but are usually spread out to help in supporting 

 the animal when resting in the water: they come into 



