EEPT1LES. 



303 



tiary strata of our island, that the temperature of the north 

 of .Europe, during the tertiary epoch, was warmer than in our 

 day. The physiological reasons already stated, in our general 

 remarks on the class, prove that it would be impossible for 

 serpents of the size of Palceopliis to live in the present climate 

 of the south of England. 



Fourth Order. BATRACHIA. Form a well-defined group 

 of reptiles. On their escape from the egg, they present an 

 organisation which resembles fishes. They breathe by gills ; 

 lead an aquatic life ; and soon pass through a series of 

 changes, by which they lose the gills, acquire feet and lungs, 

 and are metamorphosed into perfect Batrachia, of which the 

 frog and salamander are types. In addition to this physiolo- 

 gical character, their skeleton differs from other reptiles. The 

 skull is flat ; the teeth, when they exist, are small, sharp, 

 -and nearly equal throughout ; the ribs are absent, or are 



FIG. 208. Rana temporaria. 



merely rudimentary. "We divide the order into two families, 

 characterised by the presence or the absence of a tail. 



