THE INTERNAL EAR 751 



sound, it has been seen that this is due to the form of sonorous vibra- 

 tions ; and that musical sounds usually are compound, their quality de- 

 pending largely on the relative loudness of the harmonics, partial tones 

 etc. It has also been seen that resonant bodies may repeat by influence, 

 not only the actual pitch of tones, but their quality. If there is in the 

 cochlea an anatomical arrangement of rods or fibres by which the 

 sonorous vibrations conveyed to the ear are repeated, there is reason to 

 believe that the quality as well as the pitch is reproduced. 



The arrangement of the rods entering into the structure of the organ 

 of Corti and of the fibres of the membrana basilaris has afforded a theo- 

 retical explanation of the final mechanism of the appreciation of pitch. 

 With the exception of the internal ear, the action of different portions 

 of the auditory apparatus is simply to conduct and repeat sonorous 

 vibrations ; and the sole use of these accessory parts, aside from the 

 protection of the organs, is to convey the vibrations to the terminal 

 nervous filaments. Whatever may be the uses of the membrana tympani 

 in repeating souhds by influence, it is certain that this membrane pos- 

 sesses no true auditory nerves, and that the auditory nerves only are 

 capable of receiving impressions of sound. Thus, hearing, and even the 

 appreciation of pitch, is not necessarily lost after destruction of the 

 membrana tympani ; and if sonorous vibrations reach the auditory nerves, 

 they will be appreciated and appreciated correctly. 



In view of the arrangement of the organ of Corti, with its eleven 

 thousand or more rods of different lengths arranged with a certain 

 degree of regularity, a number more than sufficient to represent all the 

 notes of the musical scale, it is not surprising that they should be re- 

 garded as capable of repeating all the notes heard in music. Helmholtz 

 formulated this idea in the theory that sounds conveyed to the cochlea 

 throw into vibration only those elements of the organ of Corti which are 

 tuned, so to speak, in unison with them. According to this hypothesis, 

 the rods of Corti constitute a harp of several thousand strings, played 

 on, as it were, by the sonorous vibrations. Theories analogous to that 

 proposed by Helmholtz, but of course lacking the basis of exact anatom- 

 ical and physical details developed by modern researches and experi- 

 ments, were advanced by Du Verney (1683) and by Le Cat (1767). 



Viewing the question anatomically, it is by no means certain that the 

 rods of Corti are so attached and stretched that they are capable of 

 separate and individual vibrations. It has not been demonstrated that 

 certain of these rods vibrate under the influence of certain notes or that 

 they are tuned in accord with certain notes. Hensen and others have 

 rejected the theory of Helmholtz, basing their opinions mainly on the 

 anatomical arrangement of the organ of Corti. Hensen assumed it to be 



