on the Membrana Tympani. 11 



tympani by the muscles of the malleus, being considered as in- 

 capable of answering that purpose. 



Thi? slight sketch of the organ of hearing, and of the uses, 

 as they are generally understood, of the different parts, will 

 enable me to point out, with more clearness, what parts of the 

 theory appear defective, and what improvements may be made 

 on it. 



It is true that the membrana tympani is stretched and re- 

 laxed by the action of the muscles of the malleus, but not for 

 the purpose alleged in the commonly received theory. It is 

 stretched, in order to bring the radiated muscle of the membrane 

 itself into a state capable of acting, and of giving those diffe- 

 rent degrees of tension to the membrane which empower it to 

 correspond with the variety of external tremors : when the 

 membrane is relaxed, the radiated muscle cannot act with any 

 effect, and external tremors make less accurate impressions. 



The membrana tympani, with its tensor and radiated muscles, 

 may be not unaptly compared to a monochord, of which the 

 membrana tympani is the string ; the tensor muscle the screw, 

 giving the necessary tension to make the string perform its 

 proper scale of vibrations ; and the radiated muscle acting upon 

 the membrane like the moveable bridge of the monochord, ad- 

 justing it to the vibrations required to be produced. The com- 

 bined effects of the action of these muscles give the perceptions 

 of grave and acute tones ; and, in proportion as their original 

 conformation is more or less perfect, so will their actions be, 

 and, consequently, the perceptions of sound which they com- 

 municate. 



This mode of subdividing the motions of the membrana 

 tympani between two sets of muscles, allotting a portion to 



C 2 



