70 



THE COMMON FROG. [chap. 



median process, reminding us of the odontoid pro- 

 cess of the axis. 



The frog, as has been said, has no ribs, in spite of 

 the long " transverse processes " which project out on 

 each side of the backbone. Ribs are not necessary 

 to it, for it could apply them to none of the purposes 

 to which ribs are ever applied. 



In all beasts ribs aid importantly in respiration, 

 serving by their motions alternately to inflate or' 

 empty the lungs by enlarging or contracting the 

 cavity of the chest in the way before m.entioned. 

 The frog, however, breathes exclusively, as regards 

 the lungs, by swallozving air by a mechanism which 

 will be described shortly. 



In serpents the ribs are the organs of locomotion, 

 as also in the Flying Dragon before referred to ; but 

 in frogs locomotion is effected exclusively by the 

 limbs. In the very aberrant species, Pipa and Dac- 

 tylethra, there are on each side of the anterior parts 

 of the body two enormously long transverse processes, 

 each process bearing at its extremity a short flattened, 

 straight osseous or cartilaginous rib. These little ribs 

 can, however, take no part in such functions as those 

 just referred to. 



Ribs, moreover, are found in the other existing 

 orders of the frog's class, i c. both in the Urodcla and 

 OphiomorpJia. In none, however, do they join a 

 breast-bone, or sternum, another character in which 

 Batrachians agree with fishes, though they ditfer from 

 fishes in that they have a sternum at all. In ascend- 

 ing from fishes through the Vertebrate sub- kingdom, 

 a sternum first appears in the class Batrachia, 



