VI.] THE COMMON FROG. 85 



joints than three, while, in some lizards, the fourth 

 digit may have as many as five joints. 



Fig. 50. — Dorsal surface of skeleton of right hand of the Tortoise, CheJydra (aftei 

 Gegenbaur). c, cuneiforme ; in, intermedium (or centrale) ; /, lunare ; m^ — ;«5, 

 metacarpals ; r, radius ; s, scaphoides ; «, ulna ; i — 5, the five distal carpals, 

 namely— I, trapezium ; 2, trapezoides ; 3, magnum; 4 and 5, divided unciforme. 



In the frog the wrist-bones (called respectively the 

 magnum and unciforme) which support the third, 

 fourth, and the little fingers, are formed together into 

 a single ossicle. The same condition, however, some- 

 times occurs even in the orang. On the other hand, 

 the single bone which in man and beasts supports 

 both the '' ring " and the " little " fingers, may be re- 

 presented by two ossicles in the frog's class (as e.g. in 

 Salamandra) and in some reptiles (as e.g. in Chelydrd). 



No member of the frog's class which has an arm at 

 all, bears less than two fingers (as in Proteus) upon 

 it. Thus we meet with a number as small as that 

 which is developed amongst beasts in ruminants, but 

 not so small a number as in the horse. ■ 



In the rudimentary condition of its thumb the frog 

 participates in a very common defect, since this 

 member is absent in very many forms. It is so even 

 in creatures as highly organised and as like man in 

 bodily structure as monkeys, since both the spider- 



