THE AHaUMENT APPLIED. 39 



to this cavity a communication with the external air. In 

 one word, it exactly answers the purpose of the hole in a 

 drum. 



The membrana tympani itself, likewise, deserves all the 

 examination which can be made of it. It is not found :ji 

 the ears of fish ; which furnishes an additional proof of what 

 indeed is indicated by every thing about it, that it is appio- 

 priated to the action of air, or of an elastic medium. It 

 bears an obvious resemblance to the pelt or head of a drum, 

 from which it takes its name. It resembles also a drum- 

 head in tliis principal property, that its use depends upon its 

 tension Tension is the state essential to it. Now we know 

 that, in a drum, the pelt is carried over a hoop, and braced 

 as occasion requires, by the means of strings attached to its 

 circumference. In the membrane of the ear the same pur- 

 pose is provided for more simply, but not less mechanically 

 nor less successfully, by a difierent expedient, namely, by 

 the end of a bone — the handle of the malleus — pressing upon 

 its centre. It is only in very large animals that the texture 

 of this membrane can be discerned. In the Philosophical 

 Transactions for the year 1800, vol. 1, Mr. Everard Home 

 has given some curious observations upon the ear, and the 

 drum of the ear of an eleiiliant. He discovered in it what 

 he calls a radiated muscle — that is, straight muscular fibres 

 passing along the membrane from the circumference to the 

 centre — from the bony rim which surrounds it towards the 

 handle of the malleus, to which the central part is attached. 

 This muscle he supposes to be designed to bring the mem- 

 brane into unison with difierent sounds ; but then he also dis- 

 covered that this muscle itself cannot act, unless the mem- 

 brane be drawn to a stretch, and kept in a due state of tight- 

 ness by what may be called a foreign force, namely, the 

 action of the muscles of the malleus. Supposing his expla- 

 nation of the use of the parts to be just, our author is weL 

 founded in the reflection which he makes upon it, "that 

 this mode of adapting the ear to different sounds, is one of 



