of the Membrana Tynipanu 3^5 



fmall bones which are attached to it ; and thus, in the organ 

 of hearing, each part is admirably adapted, not only to the 

 purpofe for which it is defigned, but alfo as a provifion 

 againft accident or difcafe ; fo that, whenever any particular 

 part is deftroyed, another is fubftituted for it, and the organ, 

 from this deprivation, fuffcrs but little injury in its functions. 



It feems that the principal ufe of the membrana tympani 

 is, to modify the impreffions of founds and to proportion 

 them to the powers and expectation of the organ. Mr. P. 

 had loll this power for a confiderable period after the deftruc- 

 tion of the membrane; but, in procefs of time, as the ex- 

 ternal ear acquired the additional motions I have defcribed, 

 founds were rendered ftronger or weaker by them. When, 

 therefore, he was add re fled in a whifper, the ear was feen 

 immediately to move; but, when the tone of voice was 

 louder, it then remained altogether motionlefs. 



Some additiondl Remarks, on the Mode of Hearing in Cafes 

 where the Membrana Tympani has been dejlroycd. By 

 Evkrard Home, Efq. 



After having communicated to this learned Society the 

 very curious fails contained in Mr. Cooper's paper, which 

 prove that the organ of hearing is capable of receiving all 

 the different impreffions of found, when the membrana 

 tympani has been deftroyed, it may not be improper to 

 explain, from the obfervatious contained in a former paper 

 on this fubjeel, in what manner this may take place. 



It is there ftated, that any vibrations communicated di- 

 rectly to the bones of the fkull, are as accurately impreffed 

 upon the organ, as through the medium of the membrana 

 tympani. The office of that membrane is therefore to afford 

 an extended furface, capabl-; of receiving impreffions from 

 the external air, and of communicating them to the finall 

 bones of the ear; which a membrane would be incapable of 

 doing, unlefs it had a power of varying its tenfion, to a^apt 

 it to different vibrations. 



In the above cafe's, in which this membrane, the malleus, 

 and the incus, had been deftroyed, it would appear that the 

 tfapes was ac\ed upon by the air received into the cavity of 



Vol. VIII. 3B the 



