420 CLASS REPTILIA. 



others experience in the skin of the anterior feet very nota- 

 ble changes, which seem to be made for the purpose of ena- 

 bling them to retain the female more closely. 



All the batracians in their first state can swim ; some even 

 appear to remain all their lives under the tadpole form, 

 only that they then possess both lungs and gills. The ma- 

 jority walk upon the earth, climb, and even leap with facility. 

 The form of their body varies considerably and indicates as 

 it were beforehand the nature of their movements. Thus, 

 for example, all the batracians which preserve the tail in 

 their latest state, walk slowly, can merely drag their bodies 

 along the ground, and live usually in the water : such are 

 the salamanders, the protei, and the sirens. Those, on the 

 contrary, which lose this member, as the frogs, hylse, and 

 toads, walk on the ground, climb trees, and leap perfectly 

 well. 



We may conceive that the osseous frame- work of these ani- 

 mals must present considerable differences. Their spine con- 

 sists of a series of vertebrae not very distinguishable from each 

 other ; the bones of the head, or rather their forms, present 

 differences still more marked. The head, in general, has little 

 mobility, and is articulated in a single point by the assist- 

 ance of a tubercle, or condyle with three facets. The bones 

 of the upper jaw are always united together by synostosis, 

 and are not dilatable. Some species have no ribs whatever, 

 and very short ones are observable in some genera. The 

 number of feet varies ; sometimes only the front feet are 

 visible, but most generally there are four. Their respective 

 length differs according to the genera, as also does the num- 

 ber of toes. The batracians have very strong and very 

 irritable muscles ; a notorious example of this is to be found 

 in the thighs of frogs. These animals exhibit many other 

 peculiarities in their locomotive organs, which we shall have 

 occasion to notice in treating of the genera. 



