MECHANISM OF HEABING 



305 



the scala vestibuli. This movement is transmitted through 

 the membrane of Reissner to the endolymph and to the 

 basilar membrane, and from these to the scala tympani, 

 the result being a bulging outwards of the fenestra rotunda. 

 It is usually beheved that the auditory nerve is stimu- 

 lated by vibrations of the basilar membrane, which cause 

 the hairs of the hair-cells to move and possibly to touch 

 the membrana tectoria. 



As to the way in which sounds of different pitch are 

 recognised, the most satisfactory hypothesis is that put 



B.M 



Fig. 53.— End-organ of the auditory nerve (from Starling's Principles 

 of Physiology) : B.M., basilar membrane ; C, canal of Corti ; R.C., 

 rods of Corti; I.H., O.H., inner and outer hair-cells; S.C., 

 sustentacular cells ; Au., auditory nerve ; m.t., membrana tectoria. 



forward by Helmholtz, who regarded the basilar membrane 

 as a series of resonators each responding to a certain 

 periodicity of vibration. In favour of this view is the 

 fact that when the short fibres of the membrane are de- 

 generated, as in boilermakers' disease, there is inability to 

 hear high notes. In other conditions there may be deaf- 

 ness to some notes, not to others. Further, the ear can 

 be fatigued to one note, leaving its appreciation of other 

 notes unaffected. 



CENTRAL CONNECTIONS OF THE AUDITORY NERVE 



The cochlear division of the eighth nerve has its cell- 

 body in the spiral ganglion of the cochlea. The axons of 

 "20 



