On tie StruElure and Ufes of the Memhrana Tytiipar.!, ^^ 



The membrana tympani, and every other part of the organ, were found to be much 

 larger in proportion than in other quadrupeds, or in man ; differing in this refpeft from the 

 eye of the elephant, which is unufually fmall, v.hen compared with the enormous bulk of 

 the animal. 



The membrane was found of an oval form ; the (hort diameter of the oval rather more 

 than an inch in length ; the long diameter an inch and -/^ths. 



In the human ear, the membrana tympani is nearly circular; the longed diameter is- 

 -^gths of an inch ; the fliorteft ^'oths. 



As the membrane in the elephant exceeds that of the human ear in thicknefs as much as 

 in extent, which is as the fquares of their diameters, or in the proportion of 135 to 14, it 

 isnatural to conxlude that the mufcular fibres which are to ftretch the one, muft greatly 

 exceed in ftrength thofe capable of producing the fame degree of tenfion in the other. 



From this (latement, the mufcular fl:ru£lure in the human membrana tympani will 

 nec^flarjly be fo much lefs diftindt than in the elephant, as fcarcely to be viCble to the naked 

 eye, and will eafily be overlooked by the mod attentive obferver, who is not dire£ted by 

 fome previous information to examine it under the moft favourable circumftances ; but, 

 when thefe are attended to, it can be perceived without the aid of glaffes. 



If the membrana tympani of the human ear is completely expofed on both fides, by re- 

 moving the contiguous parts, and the circular covering is carefully waflied off from its- 

 external furface, then, by placing it in a clear light, the radiated direftion of its fibres- 

 may be eafily dete£led. If a conimon magnifying glafs is ufed, they are rendered nearly as 

 diftinft as thpfe of the elephant appear to the naked eye ; their courfe is exa£ily the fame ; 

 and they differ in nothing but in being formed upon a fmalier fcale. 



When viewed in a microfcope magnifying 23 times, the mufcular fibres are beautifully 

 confpicuous, and appear uniformly the fame throughout the whole furface, there being no 

 central tendons, as in the diaphragm ; .the mufcular fibres appear only to form the internal 

 layer of the membrane, and are moft diftinilly fecn when viewed on that fide. 



In examining this membrane in different fubje£t, the parts were frequently found in a 

 more or lefs morbid ftate. In one inftance, the membrane was found loaded with b'ood- 

 vefTels, was lefs tranfparent than ufual, and was united by clofe adhefion to the point of 

 the long procefs of the incus. In another inflance, there was a preternatual oilification 

 adhering to it, at a fmal! diftance from the end of the handle of the malleus. 



As mufcles in general are fupplied with blood-veficls in proportion to the frequency of 

 their adion, it is an objeft of importance to. determine the vafcularity X)f the membrana 

 tympani. Upon this fubjeft, ray own want of information has been amply fupplied by 

 Dr. Baillie, who, in a communication upon this fubjeft, fhowed me a preparation of the 

 membrane, in which the vefTels had been moft fuccefsfully injefted with coloured wax. 

 - In this preparation, the moft beautiful of the kind I ever faw, the vcffels in their 

 diftribution refembled thofe of the iris, and were nearly half as numerous : they anafto- 

 mokd with one another in a fimilar manner,, and their general dire£Uon was from the 

 4 cixcumferenca- 



