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TEXTBOOK OF ZOOLOGY 



The common bullfrog is ordinarily greenish or olive brown. Un- 

 derparts are mottled with dark spots on a white background, and 

 the upper surfaces may be plain or marked with large dark splotches. 

 The legs are marked with crossbars and other splotches of dark 

 color. Preserved specimens appear brownish gray with the dark 

 mottling lighter in color than on the living specimen. 



The body of the bullfrog includes the head and trunk. Attached 

 to the trunk on either side anteriorly are the forelegs and posteriorly 

 the hindlegs. 



The head has two prominent eyes which protrude above its sur- 

 face. These can be drawn back into their orbits and forced some- 



Fig. 272. — External features of the common bullfrog, Rana catesbeiana. (Courtesy 

 of Southern Biological Supply Company.) 



what into the mouth cavity. The lower lid of the frog's eye with 

 its attached nictitating membrane is drawn up over the eye, not by 

 independent movement of the eyelid, but as a result of the retraction 

 of the eye into the orbit. The upper eyelid is immovable. Back 

 of each eye is a circular oval area, the tympanum or eardrum. In 

 the females this is about the size of the eye, while in the males it 

 is larger than the eye. A small fold of skin, the tympanic fold, 

 runs from the eye around the posterior margin of the tympanum. 

 The two nostrils or nares are near the anterior part of the head, and 

 each is guarded by a valve. The mouth reaches from one side of 



