66 



ESSENTIALS OF ZOOLOGY 



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 t7'unk. Attached 

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

 the liindlegs. 



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

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

 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 



i.i"^' 



h . ■•^': ■ 



A 



B 



Fig, 18. — Melanophore from Rana temporia. A, Pigment distributed in response 

 to light; B, pigment contracted. (Redrawn and modified from Noble, Amphihia of 

 North America, McGraw-Hill Book Company, Inc.) 



of each eye is a circular oval area, the tyinpamim 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 

 the head to the other and has an upper and lower jaw. The anus 

 or vent is at the extreme posterior end of the trunk. 



The forelimbs are composed of the upper arm, which joins the 

 trunk, the forearm, wrist or carpus, and the hand with its four digits. 

 In the male, particularly during the breeding season, the innermost 



