SUMMARY OF THE MECHANISM OF AUDITION. 229 



tain that they are tuned in accord with different tones. Hen- 

 sen makes, on this point, the following statement : 



" It is now my conviction, that by the hypothesis f more 

 and more corroborated ' that the fibres of Corti constitute the 

 organ of the labyrinth tuned to the appreciation of tones, 

 our comprehension and the investigation of the internal ear 

 have taken a false direction. 



" I assert, next, that the rods of Corti cannot play the 

 important part in the appreciation of tones, which has been 

 attributed to them in the hypothesis of Helmholtz." * 



It is pretty evident that, although the theory of Helm- 

 holtz is undoubtedly the only one affording any reasonable 

 explanation of the appreciation of tones, it lacks positive 

 anatomical confirmation. And, f arthermore, we do not even 

 know the anatomical connections between the rods of Corti 

 and the filaments of the auditory nerves. 



In view of the considerations just given, we have simply 

 recited the theory of Du Yerney, Le Cat, and Helmholtz, as 

 one which may or may not be sustained hereafter by more 

 exact researches ; but at present it must be acknowledged 

 that there is no more satisfactory explanation of the mech- 

 anism of the final appreciation of musical tones. 



Summary of the Mechanism of Audition. 



The waves of sound are simply collected by the pavilion 

 of the ear and are conveyed, through the external meatus, to 

 the membrana tympani. The membrana tympani, a delicate, 

 rounded, concave membrane, receives these waves and is 

 thrown into vibration. 



The arrangement of the bones and muscles of the middle 

 ear admits of variations in the tension of the membrana 

 tympani. By increasing the tension of this membrane, the 

 ear may be rendered insensible to grave sounds, while high- 



1 HENSEN, Experimentelle Studien zur Physiologie des Gehorgans, von DR. 

 SCHMIDEKAM mil Zusatzen von DR. HENSEN. Arbeiten aus den Kieler physiologi- 

 schm Institut^ Kiel, 1869, S. 181. 



