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Elementary Biology. 



the frog, on the other hand, only the air nearest the wall of 

 the lung can be employed for respiratory purposes ; a loss, 

 however, not of much importance, since pulmonary respira- 

 tion is in the frog greatly assisted by secondary respiration 

 through the skin. The mode of inspiration in the frog 

 differs from that of the higher animals, since, instead of 



FIG. 156.- DEVELOPMENT OF THE LUNGS. (Wiedersheim.) 

 PD 



ff 



AT' 



FD, primitive intestine ; S, S', lung-sacs ; /, trachea ; b, bronchus ; 

 Lg, seconda y pulmonary sacs. 



employing the muscles of the lung and the abdominal 

 wall, &c. to bring about the distension of the lung, the frog 

 inhales by the nostrils, so filling the buccal cavity, then, 

 shutting the oesophagus and nostrils by means of the 

 muscles of the buccal wall, it forces the air into the lungs, 

 from which it is e.xpelled by the natural elasticity of the 

 lung itself. 



