CHAP, iv.] HEAEING. 1017 



tone, may be spoken of as noise. But, if noise is only confused 

 music, and music more or less orderly noise, the cochlea must 

 be a means of appreciating noises as well as musical sounds. 



We may therefore reject the view which has been put forward 

 by some that while by the cochlea we appreciate musical sounds, 

 our knowledge' of noises is gained by auditory impulses reaching 

 us through the vestibule. 



Are we to conclude then that the vestibule has nothing to 

 do with hearing, is concerned only with equilibrium ? A certain 

 support is given to this view by cases in man where deafness 

 seems to have been due to disease confined to the cochlea ; and 

 in animals deafness is said to have been produced by division of 

 the cochlear nerve, the vestibular nerve being left intact. More- 

 over animals possessing a cochlea certainly continue to hear and 

 to hear well after division of both vestibular nerves ; but this is 

 not a valid argument against no auditory impulses at all pass- 

 ing along this nerve, since the cochlea is obviously adequate by 

 itself for ordinary hearing, and the loss of the vestibule might 

 simply entail in the character of the sense changes too fine to 

 be readily recognized in a dumb animal. 



On the other hand vertebrates, lower in the scale than birds 

 and reptiles, namely, fishes, though they have a well-developed 

 vestibular labyrinth, possess either no cochlea at all or the 

 merest trace of one, and yet undoubtedly are the subject of 

 auditory sensations, in some cases of acute sensations. The 

 evidence that fishes hear seems irresistible, they are said to 

 respond to musical sounds ; and yet those who hold the views 

 just explained are driven to maintain either that fishes do 

 not hear in the true sense of the word but only feel vibra- 

 tions, or that they hear by means of an insignificant fragment 

 of their relatively large vestibule. The structure of the pis- 

 cine and amphibian vestibular auditory epithelium is in the 

 main putting aside smaller matters, such as the length of 

 the auditory hairs, the size and abundance of otoliths and oto- 

 conia and the like, so identical with that of birds and reptiles 

 and of mammals, that it is impossible to resist the conclusion 

 that it serves the same purpose in all the several classes. In 

 birds and reptiles the short rudimentary nearly straight tubular 

 cochlea possesses a short basilar membrane, an auditory epithe- 

 lium in which a distinction of outer and inner hair-cells is fore- 

 shadowed, and a tectorial membrane. But if we are to suppose 

 that these creatures receive auditory impulses exclusively from 

 the cochlea, and none at all from the vestibule, it is a matter of 

 wonder that the cochlea of the, for the most part, dumb croco- 

 dile should appear almost as highly developed as that of the 

 vocal bird. Or again, if the bird and reptile already possessing 

 a cochlea still derive auditory sensations by means of the vesti- 

 bule, we may conclude that mammals also do the same. 



