566 THE NERVOUS SYSTEM. 



organ by which we appreciate the pitch of musical sounds. According 

 to this view, the radiating fibres of the membrana basilaris are attuned, 

 by their length and tension, to different notes of the musical scale ; and 

 the vibration of each is communicated to corresponding hair cells in 

 the organ of Corti, thus reaching the terminal fibres of the auditory 

 nerve. For every note which gains admission to the internal ear, only 

 certain fibres and hair cells of the ductus cochlearis are thrown into 

 vibration, and only certain fibres of the cochlear nerve receive a sono- 

 rous impression. There is certainly an apparent similarity between 

 the fibrous and cellular elements in the organ of Corti 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 corresponding action 

 in the two cases. 



But the difficulty in attributing to the cochlea the discrimination of 

 musical notes, lies in the fact that its development in different animals 

 does not correspond with their capacity for the production and percep- 

 tion of musical sounds. The cochlea, under the form which it presents 

 in man, is confined to the mammalia. In birds this part of the audi- 

 tory apparatus is an obtusely conical eminence,* containing two small 

 cartilaginous cylinders united by a membrane representing the mem- 

 brana basilaris ; and the part corresponding with 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 reptiles and in fishes it is completely undeveloped. 



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

 internal ear, but little inferior to the same organ in man. But in sing- 

 ing birds it is comparatively rudimentary. Some of these birds may 

 be taught to repeat particular melodies, showing that their capacity 

 of discriminating musical notes is equal to their power of producing 

 them by the vocal organs. And yet that part of their auditory appa- 

 ratus which should be most highly developed according to the view in 

 question, 13 in reality the least so. If we compare a horse or a pig with 

 a thrush or a mocking-bird, it is evident that the grade of musical sen- 

 sibility in theso animals is in no relation with the development of the 

 cochlea. In fact, the cochlea of a singing bird resembles that of a croco- 

 dile or a serpont more closely than that of a quadruped or a man. At 

 the same time, the other parts of the internal ear in birds, the double 

 sac of the vestibular cavity, the membranous semicircular canals and 

 ampulla, the fenestra ovalis, and the fenestra rotunda, are all highly 

 developed ; some of them nearly or quite as much so as in mammalians. 



* 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.' 



