VI.] 



THE COMMON FROG. 



91 



it does with that which is possessed by any bird or by 

 most reptiles. 



The frogs and toads, however, differ from the 

 Urodda and present us with a pecuHar condition of 

 the ankle-bones, in that the two which represent the 

 bones of the first row are so greatly elongated as to 

 give to the limb an additional segment — as it were 

 two " long bones " more. 



We should search in vain through every other order 

 of the Batrachian class, through every known group 

 of birds and reptiles, both living and fossil, to find any 



Fig. 57. — Elongated tarsus of Leaiuroids. Left-hand figure, tarsus of Cheiyogaleus" 

 right-hand figure, tarsus of Tarsius. A, calcaneum B. cuboides, C, navi- 

 culare. 



analogous structure. None of the lowest mammals, no 

 marsupial, no rodent, no insectivorous or carnivorous 

 beast, no hoofed mammal, presents us with anything 

 of the kind. Nevertheless, at almost the other end of 

 the series, in the very highest order, that to which 



