388 



MANUAL OF ZOOLOGY. 



tail, both of which structures exist in the larva, whilst the two 

 pairs of limbs are always present. The skin is soft, and there 

 are rarely any traces of an exoskeleton. The dorsal vertebrae 

 are " proccelous," or concave in front, and are furnished with 

 long transverse processes, which take the place of ribs, which 

 are only present in a rudimentary form. The radius and ulna 

 in the fore-limb, and the tibia and fibula in <the hind-limb, are 

 anchylosed to form single bones (fig. 150). The mouth is 

 sometimes edentulous, but the upper jaw has usually small 

 teeth, and the lower jaw sometimes. The hind-limbs usually 

 have the digits webbed for swimming, and are generally much 

 larger and longer than the fore-limbs. 



Fig. 150. Skeleton of the common Frog (Ranatemporaria). ^Dorsal vertebrae, , 

 with long transverse processes. 



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 



