The Prog — An Amphibious Vertebrate Animal 439 



(Figs. 216 and 217). The auditory nerve carries the impulses to the 

 brain, where the sensation of hearing is really produced. There are no 

 external ears. The middle ear communicates with the mouth cavity by 

 means of the Eustachian tube. The latter aids in equalizing air pres- 

 sures on the eardrums. The inner ear also contains organs of equilibrium. 



Esophagus 



ClUatGd mouth of 

 oviduct 



. Egrg 



Fat body 



Ovary 



-Adrenal (j]and 



Hidney 



Ovidact 



Ureter 



.—Rectum 



Bladder 



Uterus 



Cloaca 



.Anus 



Fig. 218. — Urinogenital system of female frog (ventral view). 



The olfactory sense is located in a pair of nasal cavities lined with 

 folds of sensitive, epithelial, nasal membranes. The external nares (an- 

 terior nares) connect with the nasal cavity. The internal nares (posterior 

 nares) connect the nasal cavity with the mouth cavity. The nares in 

 amphibia and other vertebrates (above the fishes) are used for both 

 respiratory and olfactory purposes. The olfactory nerves connect the 

 epithelial nasal membranes of the nasal cavities with the olfactory lobes 

 of the brain (Figs. 216 and 217). The elevated papillae of the mouth 



