AMPHIBIOUS VERTEBRATES. 



195 



Class IV. AMPHIBIOUS VERTEBRATES. SALAMAN- 

 DERS, TOADS, etc. (Batrachid). 



General Characteristics. The Batrachians are amphibi- 

 ous Vertebrates that breathe air by perfect lungs, though 

 30me adult forms have gills. They pass through a distinct 

 metamorphosis. The higher forms have paired limbs, the 

 toes not being clawed as in the reptiles. They are gen- 

 erally oviparous. 



Skeleton. In the frog the skull is closely connected 

 with the body, and differs from that of higher Vertebrates 

 in being partly cartilaginous 

 (Fig. 237). The bones of the 

 limbs, when present, resemble 

 those of higher Vertebrates. 



Tarsus. 



Metatarsus. 



Phalanges. 



FIG. 237. Skull of the frog (Rana 

 esculenta), from below, showing 

 teeth and the cartilaginous gir- 

 dle-bone, y. 



This is shown in Fig. 238, 

 which should be compared 

 with the limb of the cat. 



Digestion. The mouth is 



generally large, and in the frog (Fig. 237) the upper jaws 

 are armed with delicate, saw-like teeth. Tadpoles have 



FIG. 238. Bones of the right 

 leg of a young toad, greatly 

 enlarged. The femur not 

 shown ; the tibia and fibula 

 are combined together. (Af- 

 ter Morse.) 



