126 Mr. R. Moon on the Structure of the Human Ear, and on 



(1) To draw backwards and stretch the membrana tympani ; 



(2) To force inwards the stapes*; 



that is, the effect of the muscles combined with the bones of the 

 ear is to produce in the stapes and membrana tympani a motion 

 opposite to that produced in them by rarefied waves of air. 



Hence, since in order that the auditory apparatus shall con- 

 tinue in the exercise of its proper functions it is essential that 

 it shall possess in itself the means of restoration to its normal 

 state after disturbance — since, as has been seen, the combined 

 bones and muscles of the ear are adequate to perform this func- 

 tion as regards rarefied waves — since no other mode of perform- 

 ing it is apparent — and since no other intelligible function has 

 ever been ascribed to this combination of bones and muscles f, 

 we are justified in concluding that that most remarkable and 

 characteristic portion of the auditory mechanism (the muscles of 

 the ear) has been provided solely with reference to the action 

 upon the organ of rarefied waves. 



It has been already stated that when the membrana tym- 

 pani moves outwards, its tendency to pull out the stapes will be 

 in some degree yielded to. The whole scheme of the contrivance 



* The late Mr. Toynbee (Diseases of the Ear, p. 177) appears to have 

 entertained the opinion that the two muscles have opposite functions. 



I think we may conclude with certainty that such cannot be the case ; 

 for otherwise, the muscles being of the voluntary class (Wilde's ' Practical 

 Observations on Aural Surgery/ 1853, p. 314), a person in the midst of 

 the most absolute silence might by a mere exercise of volition produce all 

 the effects occasioned by actual sounds. 



When the stapes is drawn home (that is, is forced as far as possible into 

 the vestibule), there can be no doubt that if the tendon of the stapedius 

 were pulled, the effect would be slightly to pull out the stapes, and at the 

 same time slightly to relax the membrana tympani. But, apart from 

 the question as to how far the muscle would act when the bone was 

 in this position, it is evident that if instead of being driven inwards the 

 stapes had been forced outwards, as it would be by the action of rarefied 

 waves, any action of the stapedius muscle consequent thereupon would be 

 to draw the stapes inwards and to stretch the membrana tympani. 



A careful consideration of the passages above cited from Mr. Wharton 

 Jones will show that when the tensor tympani is exercised, the effect, 

 amongst other things, is to produce a pressure on the anterior extremity of 

 the vestibular fenestra and a slight rotation upon it, to counteract which is, 

 in the perfect ear, the special function of the muscle of the stapes. 



f Mr. Toynbee considered, and others have concurred with him in this 

 opinion, " that the function of the tensor tympani muscle is to protect the 

 membrana tympani and the labyrinth from injury by loud sounds." 

 (Diseases of the Ear, p. 179.) Since the action of the tensor tympani takes 

 place in the same direction as the action (if any) of condensed waves, it 

 is not easy to see how the tensor tympani could diminish the effect of the 

 latter on the membrana tympani and labyrinth. On the other hand, 

 since the action of rarefied waves on the tympanum is opposite to that 

 of the tensor tympani, we can comprehend how, when rarefied waves are 

 incident, the tensor tympani might operate to mitigate their effect. 



