268 Life and Health 



about one-twentieth of an inch in width, making a curve 

 of about one-quarter of an inch in diameter. They pass 

 out from the vestibule, and, after bending around somewhat 

 like a hoop, return again to the vestibule. Each bony 



canal has a swelling at the end 

 where it opens into the vestibule. 

 This is called the ampulla. 

 J422. The Cochlea. The coch- 

 lea, or snail's shell, is another 

 chamber hollowed out in the 

 FIG. 143. Section of Cochlea, solid bone. It is coiled on 

 (From A straight downwards is the itself somewhat like a snail's 

 direction of the central column, to s h e ll. There is a central pillar, 



which E points. B points to the i i 



projecting ridge, almost dividing around which winds a long spiral 

 the canal of the tube into an canal. One passage from the 



upper compartment, D. and a .... 



lower, c.) cochlea opens directly into the 



vestibule ; the other leads to 



the chamber of the middle ear and is separated from it by 

 the little round window already described. 



The cochlea contains thousands of the most minute cords, 

 known as the fibers or organ of Corti. Under the micro- 

 scope they present the appearance of the keyboard of a 

 piano. These fibers appear to vibrate in sympathy with the 

 countless shades of sounds which penetrate the ear. From 

 the hair-like processes on these tightly stretched fibers, 

 auditory impulses appear to be transmitted to the brain. 

 > 423. The Membranous Sac. The tubes and chambers 

 of the inner ear enclose and protect a delicate membranous 

 sac of exactly the same shape as themselves. Between the 

 bony walls of the passages and the membranous bag inside 

 is a thin, clear fluid, the perilymph. The membranous sac 

 itself contains a similar fluid, the endolymph. In this fluid 

 are found some minute crystals of lime, like tiny particles 



