CHAPTER IX. 



USES OF DIFFERENT PARTS OF THE AUDITORY APPARATUS. 



Uses of the external ear Structure of the membrana tympani Uses of the 

 membrana tympani Variations in tension Vibrations of the membrane 

 by influence Destruction of the membrana tympani Appreciation of the 

 pitch of tones Mechanism of the ossicles of the ear Articulations and at- 

 . tachments of the ossicles Physiological anatomy of the internal ear Gen- 

 eral arrangement of the membranous labyrinth Vestibule Semicircular 

 canals Cochlea Liquids of the labyrinth Distribution of nerves in the 

 cochlea Organ of Corti Functions of different parts of the internal ear 

 Functions of the semicircular canals Functions of the parts contained in 

 the cochlea Summary of the mechanism of audition. 



THE uses of the pavilion of the ear and of the external 

 auditory meatus are sufficiently apparent. The pavilion 

 serves to collect the waves of sound, and probably inclines 

 them toward the external meatus as they come from various 

 directions. Though this action is simple, it undoubtedly has 

 a certain degree of importance, and the various curves of 

 the concavity of the pavilion tend more or less to concen- 

 trate the sonorous vibrations. Such has long been the opin- 

 ion of physiologists, and this seems to be earned out by ex- 

 periments in which the concavities of the external ear have 

 been obliterated by wax. 1 There is, probably, no resonance 

 or vibration of much importance until the waves of sound 

 strike the membrana tympani. The same remarks may be 

 made with regard to the external auditory meatus. "We do 

 not know precisely how the obliquity and the curves of this 

 canal affect the waves of sound, but we may suppose that the 

 deviation from a straight course protects, to a certain degree, 



1 LONGET, Traite de physiologic, Paris, 1869, tome Hi., p. 14. 



