554 THE HUMAN BODY. 



inelastic, and suppresses the vibrations as soon as the mov- 

 ing force ceases. 



Function of the Vestibule and Semicircular Canals. 

 Many noises are merely spoiled music; they are due to tones 

 so combined as not to give rise to periodic vibrations; these 

 are probably heard by the cochlea. If a single violent 

 air-wave ever cause a sound sensation (which is doubtful 

 since any violent push of an elastic substance, such as the 

 .air, will cause it to make several rebounds before coming to 

 rest) we perhaps hear it by the vestibule; the otoliths, there 

 in contact with the auditory hairs, are imbedded in a 

 tenacious gummy mass quite distinct from the proper 

 endolymph, and are not adapted for executing regular 

 vibrations, but they might yield to a single powerful impulse 

 and transmit it to the hair -cells, and through them 

 stimulate the nerves. There is reason to believe that the 

 semicircular canals have nothing to do with hearing; their 

 supposed function is described in Chapter XXXV. 



Auditory Perceptions. Sounds, as a general rule, do 

 not seem to us to originate within the auditory apparatus; 

 -\ve refer them to an external source, and to a certain extent 

 can judge the distance and direction of this. As already 

 mentioned, the extrinsic reference of sounds which reach the 

 labyrinth through the general skull-bones instead of through 

 the tympanic chain is imperfect or absent. The recogni- 

 tion of the distance of a sounding body is possible only when 

 the sound is well known, and then not very accurately; from 

 its faintness or loudness we may make in some cases a 

 pretty good guess. Judgments as to the direction of a 

 sound are also liable to be grossly wrong, as most persons 

 have experienced. However, when a sound is heard louder 

 by the left than the right ear we can recognize that its 

 source is on the left; when equally with both ears, that it is 

 straight in front or behind; and so on. The concha has per- 

 haps something to do with enabling us to detect whether 

 a sound originates before or behind the ear, since it collects, 

 and turns with more intensity into the external auditory 

 meatus, sound-waves coming from the front. By turning 

 the head and noting the accompanying changes of sensation 



