8 Mr. Home's Lecture 



centre. In the horse, deer, and cat, which have the membrane 

 still more oval than the elephant, the handle of the malleus is 

 situated in the long axis of the membrane, with its extremity 

 extending beyond the centre, reaching nearer to the circumfe- 

 rence ; and the fibres of the radiated muscle are not only at- 

 tached to its end, but also laterally to nearly the whole length 

 of its handle. 



This oval form of the membrana tympani, in those quadrupeds, 

 and the very extensive attachment of the fibres of the radiated 

 muscle to the handle of the malleus, may be the reason why 

 their ears are not equally fitted to hear inarticulate sounds, as 

 the ears of birds and of man. 



Should this radiated muscle of the membrana tympani (which 

 is probably the smallest in the body that has a distinct action) 

 be thought too insignificant to have an office of so much con- 

 sequence assigned to it, let it be remembered, that the size of 

 muscles is no indication of their importance, but only of the 

 resistance to be overcome by their action ; and that the more 

 delicate actions are performed universally in the body by very 

 small muscles, of which the iris in the eye furnishes a very con- 

 spicuous example. 



Before the mode in which the radiated muscle adapts the 

 membrana tympani to different sounds can be explained, it is 

 necessary that the more important parts of the organ should be 

 enumerated, and the use commonly assigned to each of them 

 pointed out. 



In man and the more perfect quadrupeds, this organ consists 

 of the following parts : the membrana tympani, situated be- 

 tween the external passage and the cavity of the tympanum ; 

 four small b^nes, which form a chain across the tympanum, 



