APPLICATION OF THE ARGUMENT. 27 



<lerstand the action, the use, or the mutual dependency of 

 its internal parts Its general form, however, both external 

 and internal, is sufficient to show that it is an instrument 

 adapted to the reception of sound ; that is to say, already 

 knowinsf that sound consists in pulses of the air, we per- 

 ceive, in the structure of the ear, a suitableness to receive im- 

 pressions from this species of action, and to propagate these 

 impressions to the biain. For, of what does this structure 

 consist ? [PI. V. fig. 1.] An external ear, (the concha) calcu- 

 lated, like an ear-trumpet, to catch and collect the pulses of 

 which we have spoken ; in large quadrupeds, turnmg to 

 the sound, and possessing a configuration, as well as mo- 

 tion, evidently fitted for the office : of a tube which leads 

 into the head, lying at the root of this outward ear, the 

 lolds and sinuses thereof tending and conducting the air 

 towards it : of a thin membrane, like the pelt of a drum, 

 stretched across this passage upon a bony rim : of a chain 

 of moveable, and infinitely curious, bones, forming a com- 

 munication, and the only communication that can be ob- 

 served, between the membrane last mentioned, and the in- 

 terior" channels and recesses of the skull : of cavities, sim- 

 ilar in shape and form to wind instrum.ents of music, being 

 spiral or portions of circles : of the eustachian tube, like 

 the hole in a drum, to let the air pass freely into and out of 

 the barrel of the ear, as the covering membrane vibrates, or 

 as the temperature may be altered : the whole labyrinth 

 hewn out of a rock : that is, wrought into the substance of 

 the hardest bone in the body. This assemblage of con- 

 nected parts constitutes together an apparatus, plainly 

 enough relative to the transmission of sound, or of the im- 

 pulses received from sound, and only to be lamented in not 

 being better understood. 



The communication within, formed by the small bones of 

 the ear, is, to look upon, more like what we are accustomed 

 to call machinery, than any thing I am acquainted with in. 

 animal bodies. [PI. V. fig. 2.] It seems evidently designed 

 to continue towards the sensorium the tremulous motions 

 which are excited in the " membrane of the tympanum," or 

 what is better known by the name of the " drum of the ear." 

 The compages of bones consist of four, which are so dispos- 

 ed, and so hinge upon one another, as that, if the membrane, 

 the drum of the ear, vibrate, all the four parts are put in 

 motion together ; and, by the result of their action, work 

 the base of that which is the last in the series, upon an 

 fSperture which it closes, and upon which it plays, and 



