232 



FROGS, TOAUS, AND SALAMANDERS 



motion, the body being propelled by the powerful strokes 

 of the hind legs aided by the webbed feet. 



Alimentary canal. — The mouth opens into the wide 

 gullet which, in turn, leads to the long stomach. The 

 stomach narrows posteriorly into the intestine, which makes 

 several turns and ends m an expanded portion, the cloaca 

 (Fig. 162). The kidneys, oviducts, and bladder open into 

 the cloaca. The lobed liver communicates with the an- 



Backb one Oviduc t Spinal cord__^g^^-^ 



■Tongue 



Liver 

 Pancreas 



Fig. 162. — Internal structure of a frog. 



terior part of the intestine through the duct of its gall 

 bladder. A pancreas is also present, the duct of which 

 opens into the duct of the gall sac. 



Excretory organs. — There are two reddish brown kid- 

 neys lying on the dorsal- side of the bodj' cavity near the 

 cloaca. Each one opens into the dorsal side of the cloaca 

 through a tube, the vreler. The bladder is found on the 

 ventral side of the cloaca (Fig. 162). The lungs and ,?kin 

 do their share of excretion by getting rid of the carbon 

 dioxide from the blood. 



The circulation of the frog, — The frog has a closed cir- 

 culation and the heai-t is the principal organ of the circu- 



