Chap, iv.] 



HEARING. 



1009 



nel for impulses other than auditory impulses, for impulses 

 which take part in the development of, and in the maintenance 

 of, the sense of equilibrium. We have further seen reason to 

 think that the whole of the vestibular division of the nerve, the 

 part which is connected with the maculae of the utricle and sac- 

 cule (Figs. 178, 179) as well as the part which is connected with 

 the crista? of the semicircular canals, acts in this way. But there 

 is no reason to think that, in the higher animals possessing a 



Air 



Coch. 



Fig. 179. The Membranous Labyrinth and the Endings of the Auditory 



Nerve. 



The figure is wholly diagrammatic, and is introduced as giving a simpler view 

 of the essential parts of Fig. 178 ; it should be used only in conjunction with that. 



U. utricle. S. saccule. A.S.C. Superior (or anterior) , P. S. C. posterior, 

 H.S.C. horizontal, semicircular canals. 



Coch. The canalis cochlearis represented as a tube partially unrolled, c. 

 canalis reuniens, joining the saccule with the canalis cochlearis. a.v. ductus 

 endolymphaticus, shewing its origin from both saccule and utricle, and its 

 dilated blind end, the saccus endolymphaticus. 



A.N. The auditory nerve ending in the cristse of the ampullae, in the maculae 

 of the utricle and saccule, and along the whole length of the canalis cochlearis. 

 The branch of the vestibular division of the nerve ending in the saccule remains 

 in close contact with the cochlear division, longer than does the rest of the vesti- 

 bular division ending in the utricle and ampullae (the branch to the posterior 

 canal should have been represented as lying in contact with that to the saccule). 



well-developed cochlea, the cochlear division of the nerve, dis- 

 tributed solely to the cochlea, has any such function ; this divis- 

 ion of the nerve seems to carry auditory impulses only. We 

 may therefore in the first instance confine ourselves to the coch- 

 lea exclusively. Now 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 develop- 

 ment of auditory impulses. This view is supported by the anal- 

 ogy of vision ; for we have seen reason to think that visual 

 impulses begin in the rods and cones, which like the hair-cells are 



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