FUNCTIONS OF THE LABYRINTH. 541 



The sound being conducted to the labyrinth by two paths, will, 

 of course, produce so much the stronger impression ; for undu- 

 lations will be thus excited in the fluid of the labyrinth from 

 two different though contiguous points ; and by the crossing of 

 these undulations stationary waves of increased intensity will 

 be produced in the fluid. Miiller's experiments show that the 

 same vibrations of the air act upon the fluid of the labyrinth 

 with much greater intensity through the medium of the chain 

 of auditory bones and the fenestra oval is than through the 

 medium of the air of the tympanum and the membrane closing 

 the fenestra rotunda : but the cases of disease in which the 

 ossicula have been lost without loss of hearing, prove that sound 

 may also be well conducted through the air of the tympanum 

 and the membrane of the fenestra rotunda. 



Functions of the Labyrinth. 



The fluid of the labyrinth is the most general and constant 

 of the acoustic provisions of the labyrinth. In all forms of 

 organs of hearing, the sonorous vibrations affect the auditory 

 nerve through the medium of liquid the most convenient 

 medium, on many accounts, for such a purpose. 



The function usually ascribed to the semicircular canals is 

 the collecting in their fluid contents, the sonorous undulations 

 from the bones of the cranium. They have probably, also, in 

 some degree, the power of conducting sounds in the direction 

 of their curved cavities more easily than the sounds are carried 

 off by the surrounding hard parts in the original direction of 

 the undulations, though this conducting power is in them much 

 less perfect than in tubes containing air. 



Admitting that they have these powers, the increased inten- 

 sity of the sonorous vibrations thus attained will be of advan- 

 tage in acting on the auditory nerve where it is expanded in 

 the ampullae of the canals, and in the utriculus. Where the 

 membranous canals are in contact with the solid parietes of 

 the tubes, this action must be much more intense. But the 

 membranous semicircular canals must have a function inde- 

 pendent of the surrounding hard parts ; for in the Petromyzon 

 they are not separately inclosed in solid substance, but lie in 

 one common cavity with the utriculus. 



The crystalline pulverulent masses in the labyrinth would re- 

 inforce the sonorous vibrations by their resonance, even if they 

 did not actually touch the membranes upon which tjie nerves 

 are expanded ; but, inasmuch as these bodies lie in contact 

 with the membranous parts of the labyrinth, and the vestibur 

 lar nerve-fibres are imbedded in them, they commupicate to 



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