Chap. vhi.J 



OF THE SENSE OF HEARINa. 



41S 



the nervous fibres do not vibrate after the manner of strings, and 

 the portion of each of these fibres, included in the partition of 

 the cochlea, represents only a very small part of the total fibre. 

 The analogy is therefore forced. There is nothing to prove that 

 in this order of decrease each of these fibres has. the duty of seiz- 

 ing a special tone higher and higher, and the construction of the 

 cochlea mav be nothing more than an organical device having the 



Fio. 77. 



Vertical section of tlie cochlear of a fcetas of calf. The central stem or columella and the 

 spiial lamina are not yet ossified. We see distinctly in each spiral binding the three 

 cavities as well as the thickening due to the organ of Corli. 



advantage of furnishing to the extension of the nervous threads a 

 surface relatively large under a small volume. It is not the less 

 certain that the ear of man discerns musical tones and semitones 

 with great facility; but observations of pathological anatomy 

 prove that this faculty of appreciating musical tones can persist 

 after the destruction of the cochlea. Finally, as we have had occa- 

 sion to remark in passing, singing birds have no spiral cochlea. 



Let this be as it may, the ear can seize an infinite variety 

 of tones of every kind, apart from the musical sounds, the 

 number of which is somewhat limited. As regards the wealth 

 of the sensitive field, hearing is very superior to the three 

 tactile senses, and is inferior only to the most delicate, the 

 most intellectual of the senses,, the sense of sight, 



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