on the Membrana Tympani. 7 



In a former Lecture upon the Structure of Muscles,* in 

 which a comprehensive view was taken of the subject, it was 

 stated, that the organization necessary for muscular contraction 

 could exist in an apparent membrane, and that a fasciculated 

 structure was only necessary when muscular action was to be 

 enabled to overcome resistance. The coats of the Taenia hydati- 

 gena were mentioned as an instance of the first; and the human 

 heart as the most complex of the second. In comparing the 

 membranas tympani of different animals, they afford a beautiful 

 illustration of the truth of this position. 



In birds, where from the smallness of its size the resist- 

 ance is very trifling, the membrane is very similar to the coat 

 of an hydatid, only still thinner. In the elephant, fibres form- 

 ing fasciculi are very distinct. The membrane of the horse, 

 and that of the human ear, form the intermediate gradations. 



The knowledge of a muscular structure in the membrana 

 tympani, enables us to explain many phenomena in hearing, 

 which have not hitherto been accounted for in a satisfactory 

 manner. It is principally by means of this muscle that accu- 

 rate perceptions of sound are communicated to the internal or- 

 gan, and that the membrana tympani is enabled to vary the 

 state of its tension, so-as to receive them in the quick succession 

 in which they are conveyed to it. 



In the human ear, and in that of birds, the radiated fibres of 

 the membrana tympani have their principal attachment to the 

 extremity of the handle of the malleus, which is nearly in the 

 centre of the membrane. 



In the membrane of the elephant, which is oval, the attach- 

 ment to the handle of the malleus is at some distance from the 



* Philosophical Transactions for the year 1795. 



