1 1 66 THE EAR. 



not be a pendular, but a compound vibration ; and one can readily understand 

 that, while each such compound movement always was executed in a given 

 time and through a given amplitude, it might be varied in character ; or, in 

 other words, while the time and the amplitude of the movement were constant, 

 the form of the movement might be varied to almost an infinite degree, 

 corresponding to the number and intensity of the components that produce 

 the compound movement. 



The Utricle and Saccule. 



The movements of the base of the stapes, as we have seen, may 

 vary in number, in amplitude, and in character or form, and these 

 correspond to the pitch, intensity, and quality of any tone. These move- 

 ments are communicated to the perilymph, and by it to the sacs of the 

 membranous labyrinth. As already mentioned, the utricle and saccule 

 are the first to receive the impacts, and from them the impulse is 

 transferred to the ampullae on the one hand, and to the ductus 

 cochlearis on the other. The base of the stapes is chiefly opposite to 

 the utricle, although it partly abuts against the saccule. On the wall 

 of the utricle, immediately in front, there are no nerve-endings or 

 modified epithelium, but on the back wall we find the crista acustica 

 with its characteristic bristle cells, the points of which are directed 

 towards the base of the stapes. In front of these bristle cells lie a well- 

 known mass of otoliths. The pressures must be communicated, in the 

 first instance, to the otoliths, and by them to the bristle cells. As the 

 bristle cells are fixed, while the otoliths are capable of moving backwards 

 and forwards in a fluid, it is clear that an impulse from the base of the 

 stapes may cause the otolith-mass to oscillate, and, by thus making a 

 series of impacts on the points of the bristle cells, the excitation of the 

 latter may be intensified by summation. 1 Further, the thin membrane 

 bearing the bristle cells will readily move to the impacts of the stapes, 

 and the heavy otolithic mass, by virtue of its inertia, will move more 

 slowly at first, but it will continue to oscillate, and thus keep up 

 stimulation. The long and extremely light hairs or bristles also appear 

 to be well adapted for sympathetic resonance. 2 Helmholtz points out 

 that the bristles in the crista, being of such minute mass, cannot long 

 continue in independent motion. 3 The ampullae, being relatively wide 

 cavities with narrow exits, are suitable for producing a central current, 

 which partly passes into eddies, and these would deflect the bristles, 

 causing them to oscillate. A movement of the whole mass of the bristles, 

 floating in the fluid, would not serve the same purpose. Discontinuous 

 streams of different strengths and in different directions would do so 

 effectively. 4 Others have suggested that the otoliths act as dampers ; 6 

 but when we consider that a damping mechanism is only specially 

 necessary for the perception of tones in music, and that otoliths are 

 found in the ears of animals so low in the scale as to make it improbable 

 that they appreciate such tones, this function appears to be unlikely. 



Considerable doubt still exists as to the specific functions of the 



1 Muller, "Elements of Physiology," trans, by Baly, London, 1842, vol. ii. p. 1289. 

 3 Helmholtz, "Sensations of Tone," translation by Ellis, London, 1875, p. 206. 



3 Helmholtz, ibid., p. 217. 



4 Helmholtz, Moiiatsb. d. Berl. Acad. d. Wissensch., April 23, 1868. 



5 Paul Meyer, "Etudes histologiques sur le labyrinth membraneux des reptiles et des 

 oiseaux," 1864, p. 129. 



