568 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



of the elephant, which is unusually small, when compared with the enormous bulk, 

 of the animal. The membrane was found of an oval form; the short diameter of 

 the oval rather more than an inch in length; the long diameter an inch and ^V» 

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

 is ^ of an inch; the shortest ^V- As the membrane in the elephant exceeds that 

 of the human ear in thickness as much as in extent, which is as the squares of their 

 diameters, or in the proportion of 135 to 14, it is natural to conclude that the 

 muscular fibres which are to stretch the one, must greatly exceed in strength those 

 capable of producing the same degree of tension in the other. 

 - From this statement, the muscular structure in the human membrana tympani 

 will necessarily be so much less distinct than in the elephant, as scarcely to be visible 

 to the naked eye, and will easily be overlooked by the most attentive observer, who 

 is not directed by some previous information to examine it under the most favour- 

 able circumstances; but when these are attended to, it can be perceived without the 

 aid of glasses. If the membrana tympani of the human ear be completely exposed 

 on both sides, by removing the contiguous parts, and the cuticular covering care- 

 fully washed off from its external surface; then, by placing it in a clear light, the 

 radiated direction of its fibres may be easily detected. If a common magnifying 

 glass be used, they are rendered nearly as distinct as those of the elephant appear 

 to the naked eye; their course is exactly the same; and they differ in nothing but 

 in being formed on a smaller scale. When viewed in a microscope magnifying 

 23 times, the muscular fibres are beautifully conspicuous, and appear uniformly 

 the same throughout the whole surface, there being no central tendons, as in the 

 diaphragm; the muscular fibres appear only to form the internal layer of the mem- 

 brane, and are most distinctly seen when viewed on that side. In examining this 

 membrane in different subjects, the parts were frequently found in a more or less 

 morbid state. In one instance the membrane was found loaded with blood-vessels, 

 was less transparent than usual, and was united by close adhesion to the point of 

 the long process of the incus. In another instance, there was a preternatural 

 ossification adhering to it, at a small distance from the end of the handle of the 

 malleus. 



As muscles in general are supplied with blood-vessels in proportion to the fre- 

 quency of their action, it is an object of importance to determine the vascularity of 

 the membrana tympani. On this subject my own want of information has been 

 amply supplied by Dr. Baillie, who, in a communication on this subject, showed 

 me a preparation of the membrane, in which the vessels had been most successfully 

 injected with coloured wax. In this preparation, the most beautiful of the kind I 

 ever saw, the vessels in their distribution resembled those of the iris, and were 

 neaily half as numerous; they anastomosed with each other- in a similar manner, 

 and their general direction was from the circumference to the handle of the malleus; 

 from near this handle, a small trunk sent off branches, in a radiated manner, which 

 anastomosed with those which had an opposite course. This correspondence, in 



