664 THE SENSES. 



in successive portions of the membrana basilaris are attuned, by their 

 length or tension, to vibrate in response to different notes of the musical 

 scale ; and the vibration of each set, when excited, is communicated 

 to the corresponding hair cells of the organ of Corti, and thus reaches 

 the auditory nerve fibres terminating in their substance. Thus for every 

 note sounded in the atmosphere which gains admission to the internal 

 ear, only certain fibres and hair cells of the ductus cochlearis will be 

 thrown into vibration, and only certain terminal fibres of the codilear 

 nerve will receive a sonorous impression. Some writers have even found 

 in certain parts of the organ of Corti, an apparatus for damping the 

 vibration of the fibres after the cessation of the sound, and thus prevent- 

 ing the confused intermingling of separate impressions. There is cer- 

 tainly a suggestive appearance of similarity between the long row of 

 fibrous and cellular elements m the organ of Corti, with their various 

 appendages, and the ranges of strings, capable of vibrating to different 

 notes, in a harp or piano forte ; and the similarity is sufficient to suggest 

 a certain correspondence of mechanical and physiological action between 

 the two. 



But the main difficult}^ in attributing to the cochlea, as its function, 

 the discrimination of musical notes, lies in the fact that its development 

 in different animals does not correspond with their capacity for the pro- 

 duction and perception of musical sounds. The cochlea, under the form 

 which it presents in man, is confined to the mammalia. In birds this 

 part of the auditory apparatus has not the form of a coiled spiral, but 

 is an obtusely conical eminence, 1 containing two small cartilaginous 

 cylinders united by a membrane which represents the membrana basi- 

 laris ; and the part corresponding to the organ of Corti contains only 

 nerve terminations and hair cells somewhat resembling those of the 

 inner row in mammalia ; the arch of Corti, and the three outer rows of 

 hair cells, with their cuticular covering, being absent. In serpents and 

 lizards, the cochlea is similar to that of birds ; while in the naked rep- 

 tiles and in fishes it is completely undeveloped. 



Thus, in all the mammalia, the cochlea is an important part of the 

 internal ear, apparently but little, if at all, inferior to the same organ in 

 man. But in the singing birds it is comparatively a rudimentary struc- 

 ture. Some of these birds may be taught artificially to repeat par- 

 ticular melodies, showing conclusively that their capacity of percep- 

 tion for musical notes is equal to their power of producing them by the 

 vocal organs. And yet that part of the auditory apparatus which 

 should be most highly developed in these animals, according to the view 

 in question, is in reality the least so. If we compare, for example, a 

 horse or a pig with a thrush or a mocking-bird, it is evident that the 

 grade of musical sensibility in these animals is in no relation with the 



s Owen, Anatomy of the Vertebrates. London, 1866, vol. ii. p. 134. Wagner, 

 Comparative Anatomy of the Vertebrate Animals, Tulk's Translation. New 

 York, 1845, p. 95. Waldeyer, in Strieker's Manual of Histology, Buck's Edition. 

 New York, 1872, p. 1046. 



