STRUCTURE OF THE HUMAN EAR. 



79 



the cochlea and the semicircular canals. The semi- 

 circular canals are three in number, and stand at right 

 angles to one another. No satisfactory explanation of 

 their function has yet been given ; but there is some 

 evidence that, in addition to, or apart from, hearing, 

 they are affected by the position of the head, and thus 

 serve as organs for maintaining the equilibrium of the 

 body. Each of the canals commences with an oval 

 dilatation, or ampulla. 

 In the ampulla is a 

 projecting ridge, on 

 which are long, stiff, 

 delicate, hair-like pro- 

 cesses, the vibrations 

 of which probably give 

 cprtain sound-sensa- 

 tions. In the canals 

 certain parts bear 

 shorter hairs, over 

 which are minute ear- 

 stones, or otolithe^, 

 consisting of carbonate 

 of lime, embedded in 

 a gelatinous substance. 

 The cochlea contains, 

 moreover, a compli- 

 cated and wonderful organ, discovered by Count Corti. 

 This appears to be, in fact, a microscopic musical instru- 

 ment, composed of some four thousand complex arches, 

 increasing regularly in length and diminishing in 

 height from the base to the summit of the cochlea. 

 The waves of sound have been supposed to play on 

 this organ, almost like the fingers of a performer on 

 tlie keys of a musical instrument. 



yi(r. 48. — Section tlirough the ampulla (after 

 Bernstein). N, Nerve; a^ terminal cells; h, 

 auditory hairs. 



