258 



/OOLOGY 



SECT. 



raised into a complex network of ridges abundantly supplied 

 with blood-vessels. The two lungs open anteriorly into a small 

 laryngo-tracheal chamber which communicates with the mouth by 

 the narrow slit-like glottis. The walls of the laryngo-tracheal 

 chamber are supported by a cartilaginous framework, and its 

 mucous membrane is raised into a pair of horizontal folds, the 



FIG. 877. Rana esculenta. Stomach and duodenum with liver and pancreas. DC. , DC*, common 

 bile duct ; Dc. 2 its opening into the duodenum ; d. cy. cystic ducts ; Dh., Dh.i hepatic ducts ; 

 Dn. duodenum ; G. gall-bladder ; Z, Z 1 , L~, L%, lobes of liver, turned forwards ; Lhp. duodeno- 

 hepatic omentum, a sheet of peritoneum connecting the liver with the duodenum ; M, 

 stomach ; P. pancreas ; Pi, pancreatic duct ; Py. pylorus. (From Wiedersheim's Comparative 

 Anatomy.) 



vocal chords, by the vibration of which the croak of the Frog is 

 produced. 



In breathing, the Frog keeps its mouth closed, and, by depress- 

 ing the floor of the mouth, draws air into the buccal cavity 

 through the nostrils. The floor of the mouth is then raised, the 

 nostrils, which are valvular, are closed, and the air is forced through 

 the glottis into the lungs. Thfc skin also is an important respi- 

 ratory organ. 



Circulatory Organs. The pericardium (Fig. 876, pcd.) is not 

 a separate chamber, as in Fishes, but lies in the general coslomic 

 cavity between the gullet above and the epicoracoids below; it 



