198 



BIOLOGY 



an 



FIG. 98. THE INTERNAL EAR 

 OF THE FROG 



on, auditory nerve; 

 c, semicircular canals; 



(Retzius.) 



s, saccule; 

 u, utricle. 



The inner ear, which is uhe true sensory end organ of the audi- 

 tory nerve, lies embedded in the bones of the skull. Its general 

 appearance may be seen from Figure 98. It is quite a compli- 

 cated organ, and the auditory nerve enters in and finally 



terminates in delicate endings, 

 which are readily stimulated by 

 the vibrations brought from the 

 exterior through the membrane 

 .and the columella. The canals 

 shown at c, the semicircular ca- 

 nals, have a function related to 

 balancing the body and keeping 

 it in an upright position, i. e., 

 equilibrium. 



Other senses. The sense of smell 

 is located in the nostrils. These 

 openings lead into little olfactory 



sacs just within the bones, and the air which enters them 

 passes through the bones into the mouth by openings on the 

 roof of the mouth called 

 internal nares. The ol- 

 factory nerve is expanded 

 in the olfactory sac, 

 where vapors that may 

 be in the air affect it. 



The sense of taste is 

 situated on the tongue, 

 within which are end or- 

 gans sensitive to liquids. 

 Only substances dis- 

 solved in liquids are ca- 

 pable of affecting these 

 end organs; Fig. 99. 



The touch and pressure senses are located in the skin. Scat- 

 tered over the body generally are numerous end organs, which 



FIG. 99. SECTION OF TONGUE OF FROG 



n, nerve ending; nc, nerve cells; ne, nerve trunk. 

 (Gaupp.) 



