VERTEBRATA: AMPHIBIA. 



519 





bones (fig. 282). The mouth is sometimes edentulous , but the 

 upper jaw has usually small teeth, and the lower jaw sometimes. 



Fig. 282. Skeleton of the common Frog (Rana temporarid). * Dorsal vertebrae, 

 with long transverse processes. 



The hind-limbs usually have the digits webbed for swimming, 

 and are generally much larger and longer than the fore-limbs. 

 The vertebral column is short (of ten vertebrae in the Frogs, 

 but only eight in Pipa}. The tongue is soft and fleshy, not 

 supported by an os hyoides, but fixed to the symphysis of the 

 lower jaw in front. 



In the adult Anoura, respiration is purely aerial, and is car- 

 ried on by means of lungs, which are, comparatively speaking, 

 well developed. As there are no movable ribs by which the 

 thoracic cavity can be expanded, the process of respiration is 

 somewhat peculiar. The animal first closes its mouth, and 

 fills the whole buccal cavity with air taken in through the 

 nostrils. The posterior nares are then closed, and by the con- 

 traction of the muscles of the cheeks and pharynx the inspired 

 air is forcibly driven into the windpipe through the open 

 glottis. The process, in fact, is one of swallowing ; and it is 

 possible to suffocate a frog simply by holding its mouth open, 

 and thereby preventing the performance of the above-men- 

 tioned actions. There can be no doubt, also, that the skin in 

 these animals plays a very important part in the aeration of 

 the blood, and that the frogs especially can carry on their 



