FUNCTIONS OF DIFFERENT PARTS OF THE INTERNAL EAR. 849 



idea of the arrangement of all of the structures which compose the organ of Corti. It is 

 supposed by some anatomists that the filaments of the auditory nerves terminate in the 

 cells above described ; but this point is not definitively settled. 



Functions of Different Parts of the Internal Ear. 



The precise function of the different parts which are found in the internal ear is 

 obscure, notwithstanding the careful researches that have been made into the anatomy 

 and the physiology of the labyrinth. There are several points, however, bearing upon 

 the physiology of this portion of the auditory apparatus, concerning which there can be 

 no doubt : 



First, it is certain that impressions of sound are received by the terminal filaments of 

 the auditory nerves and by these nerves are conveyed to the brain. 



Second, the functions of the parts composing the external and the middle ear are 

 simply accessory. The sonorous waves are collected by the pavilion and are conveyed 

 by the external meatus to the middle ear ; the membrana tympani vibrates under their 

 influence ; and they are thus collected, repeated, and transmitted to the internal ear, 

 under the most favorable conditions for producing a proper impression upon the auditory 

 nerves. 



In view of these facts, we must look to the functions of semicircular canals and the 

 cochlea, for an elucidation of the problem of the mechanism of the final process of audi- 

 tion ; and, in doing this, we come at once to the question of the relative importance of 

 different divisions of the internal ear. 



Functions of the Semicircular Canals. In a memoir presented to the French Acad- 

 emy of Sciences, in 1824, Flourens detailed a number of experiments upon pigeons and rab- 

 bits, in which he destroyed different portions of the internal ear. In these experiments, 

 the results of which were very definite, it was shown that destruction of the semicircular 

 canals had apparently no effect upon the sense of hearing, while destruction of the coch- 

 lea upon both sides produced complete deafness. In addition, it was observed that 

 destruction of the semicircular canals on both sides was followed by remarkable dis- 

 turbances in equilibration. The animals could maintain the standing position, but, as 

 soon as they made any movements, u the head commenced to be agitated ; and this 

 agitation increasing with the movements of the body, walking and all regular move- 

 ments finally became impossible, in nearly the same way as when equilibrium and stabil- 

 ity of movements are lost after turning several times or violently shaking the head. 1 ' 

 These observations of Flourens, at least as far as regards the influence of the semicircular 

 canals upon equilibration, have been confirmed by Goltz and are sustained by observa- 

 tions upon the human subject in the condition known as Meniere's disease. In some more 

 recent experiments, however, Boettcher assumes to have demonstrated that the semi- 

 circular canals have nothing to do with equilibration ; but all of his observations were 

 made upon frogs, in which deficiency of equilibration and of hearing would be very diffi- 

 cult to determine. As far as we can judge from experimental data, it does not seem 

 probable that the nerves directly concerned in audition are distributed to any consid- 

 erable extent in the semicircular canals. Indeed, the function of these parts is exceed- 

 ingly obscure ; for we can hardly admit, upon purely anatomical grounds, that they are 

 concerned in the discrimination of the direction of sonorous vibrations, an idea which 

 has been advanced by some physiologists. 



Functions of the Parts contained in the Cochlea. There can be no doubt with regard 

 to the capital point in the physiology of the cochlea ; namely, that those branches of the 

 auditory nerve which are essential to the sense of hearing and which receive the impres- 

 sions of sound are distributed mainly in the cochlea. When we come to analyze sonorous 

 impressions, we find that they possess various attributes, such as intensity, quality, and 

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