250 



CHARACTERS OF VERTEBRATE ANIMALS 



into a short plump body without any intervening neck-region. 

 In the adult animal there is absolutely no trace of a tail, though 

 this is well-developed in the larval form or tadpole, a fact which 

 no doubt points to the descent of Frogs from tailed ancestors. 

 The limbs are much better developed than in the Salamander, 

 but the hind-limbs, which serve both as leaping and swimming 



Fig. 155. Tailless Amphibia 

 Grass Frog (Rana temporaria], above; Common Toad (Bufo vulgaris], below. 



organs, are out of all proportion large as compared with the 

 fore-limbs. Four digits only are externally visible in the latter, 

 there being no apparent trace of a thumb, but the hind-limb 

 possesses five well-developed toes, between which a delicate web 

 extends. A very curious feature is the presence of a little horny 

 spur, the calcar, on the inner side of the foot, and examination 

 of the skeleton shows that this is really an extra digit, though in a 

 much-reduced condition. 



