THE GREEN FROG 



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lower eyelid. In front of the eyes, near the anterior end of 

 the head, are the external openings of the nostrils ; posterior 

 to the eyes are smooth, round spots, the tympanic mem- 

 branes, which are the outer portions of the frog's ears. 



The Digestive System. The wide mouth cavity (Fig. 173) 

 narrows into the short, straight esophagus. Conical teeth 

 are placed along the edge of the upper jaw and on the roof 



Fig. 172. The green frog. (Reduced) 

 Photograph by Elwin R. Sanborne, courtesy of the New York Zoological Society 



of the mouth. A thick, fleshy tongue, notched posteriorly, 

 is attached by its anterior margin to the ventral surface of 

 the mouth cavity. The tongue can be thrust out suddenly 

 to quite a distance to capture food, which consists largely 

 of insects, worms, and mollusks. Two openings lead from 

 the mouth to the nostrils, and two openings (the Eustachian 

 tubes, Fig. 173) communicate with the ears. The stomach 

 is a thick- walled sac tapering gradually into the coiled small 

 intestine. Beyond the small intestine the alimentary canal 

 suddenly increases in diameter, forming the large intestine, 



