SENSE ORGANS. 



179 



rior surface (Fig. 113). In the vestibular sac and at- 

 tached to hairlike nerve terminals there are several little 

 sandlike grains of carbonate of lime (otoliths). By mo- 

 tion of the endolymph these are shaken and affect the 

 hairlike nerve terminals, which thus become delicate 

 perceivers of the slightest movements caused by vibra- 

 tion. Again, in the ampullas the nerve fibers terminate 

 in little stiffish hairs projecting from the walls toward 

 the center like the hairs in a mule's ears (Fig. 114). 

 Vibratory shakings of the endolymph, passing up from 

 the vestibular sac through the ampulla? into the semi- 



tec 



Fig. 113. — vs, vestibule sac ; sc, membranous semicircular canals ; am, am- 

 pulla ; », nerve ; s, sacculus. 



circular canals and back to the vestibular sac, set these 

 hairs trembling, and hence they also become delicate 

 perceivers of slight vibration. 



Membranous Cochlea.— We have compared the 

 bony cochlea to a hollow stairway winding about a 

 central pillar ; now the membranous cochlea may be 

 compared to the stair in this stairway, running across 



