

CHAP. iv.J HEARING. 233 



Reissner, the endolymph of the canalis cochlearis, and the basilar 

 membrane to the scala tympani, and so reach the fenestra rotunda. 

 The bulk of the vibrations ascending the scala vestibuli thus reach 

 the scala tympani by crossing the canalis cochlearis, and in so 

 crossing affect in some way or other the auditory epithelium 

 of the organ of Corti , it is probably only a remnant which at the 

 summit of the spiral passes directly from the one scala to the 

 other. 



The features of the basilar membrane point to its being readily 

 thrown into vibrations, and we may conclude that the vibrations 

 started at the fenestra ovalis and transmitted from the scala vestibuli 

 to the scala tympani throw the basilar membrane into correspond- 

 ing vibrations. 



In the cochlea the connection of the fibres of the auditory 

 nerve seems to be exclusively limited to the hair-cells, inner 

 and outer; and we may conclude that these hair-cells are in 

 some way or other concerned in the development of auditory 

 impulses. This view is supported by the analogy of vision ; for 

 we have seen reason to think that visual impulses begin in 

 the rods and cones, which like the hair-cells are modified epi- 

 thelium cells, and we shall presently find that modified epithelium 

 cells also play an essential or important part in the development of 

 sensations other than those of vision and hearing. 



Accepting provisionally the view (we will return to the point 

 later on), that the vestibular nerve also conveys auditory impulses 

 started in the cristae and maculae, and leaning on the analogy of 

 the cochlea in which as we have just said it seems clear that the 

 hair-cells alone are connected with the auditory fibres, we may 

 conclude, in spite of the divergence of opinion as to the results of 

 histological inquiry, that in the cristae and maculae it is the hair- 

 cells also which in some way or other originate auditory impulses. 

 The relatively long hairs of the cristae, exceedingly long in some 

 of the lower animals, seem specially fitted to take up the vibra- 

 tions of the endolymph, that is to say, to be thrown into bodily 

 (transversal) vibrations and to communicate those vibrations to 

 the substance of the cell which bears them. 



It has been observed that, among the auditory hairs of the 

 Crustacea, some will vibrate to particular notes ; and as we shall 

 see presently, the vibration of particular hairs in response to par- 

 ticular tones might play an important part in the development 

 of auditory sensations. But the auditory hairs of the mammal 

 even in the cristae are far too much of the same length to permit 

 the supposition that they can act satisfactorily in this way. More- 

 over even such fitness as may seem to be present in the cristae 

 is less conspicuous in the shorter hairs of the maculae, and 

 vanishes wholly in the case of the peculiar short rods of the 

 hair-cells of the cochlea ; we can hardly imagine that the latter 

 vibrate bodily, and even in the maculae and cristae, the hairs 



