750 SPECIAL SENSES 



terminal filaments of the auditory nerves and by these nerves are con- 

 veyed to the brain. 



Second, the uses of the parts composing the external and the middle 

 ear are chiefly accessory. The sonorous waves are collected by the 

 pinna and are conveyed by the external meatus to the middle ear ; the 

 membrana tympani vibrates under their influence ; and they are thus 

 collected, repeated and transmitted to the internal ear. 



Uses of the Semicircular Canals. In the experiments of Flourens, 

 on pigeons and rabbits (1824), it was shown that destruction of the 

 semicircular canals had apparently no effect on the sense of hearing, 

 while destruction of the cochlea on both sides produced total deaf- 

 ness. In addition it was observed that destruction of the semicircular 

 canals on both sides was followed by remarkable disturbances in equi- 

 libration. The animals could maintain the standing position, but so 

 soon as they made any movements, " the head began to be agitated ; 

 and this agitation increasing with the movements of the body, walking 

 and all regular movements finally became impossible, in nearly the same 

 way as when equilibrium and stability of movements are lost after turn- 

 ing several times or violently shaking the head." These observations 

 of Flourens, at least so far as regards the influence of the semicircular 

 canals on equilibration, have been confirmed by Goltz and are sus- 

 tained by observations on the human subject, in the condition known as 

 Meniere's disease. So far as can be determined from experimental 

 data, it does not seem probable that the nerves directly concerned in 

 audition are distributed to any considerable extent in the semicircular 

 canals. Indeed, the uses of these parts is obscure ; for it can hardly be 

 admitted, on purely anatomical grounds, that they are concerned in 

 the discrimination of the direction of sonorous vibrations, an idea that 

 has been advanced by some physiologists. 1 



Uses of the Parts contained in the Cochlea. There can be no doubt 

 in regard to the capital point in the physiology of the cochlea ; namely, 

 that those branches of the auditory nerve which are essential to the 

 sense of hearing and which receive the impressions of sound are dis- 

 tributed in the cochlea. An analysis of sonorous impressions shows 

 that they possess various attributes, such as intensity, quality and pitch. 

 So far as the terminal filaments of the auditory nerve are concerned, it 

 is evident that the intensity of sound is appreciated in proportion to the 

 force of the impression made on these nerves. In regard to quality of 



1 Although the physiological literature of the semicircular canals is of immense volume, 

 little of a convincing and definite character has been learned concerning their function since 

 the observations of Flourens; and their further discussion would be out of place in this work. 

 The directions of the canals may be studied in Fig. 188, page 720. 



