THE ARGUMENT APPLIED. 37 



ducting the air towards it : of a thin membrane hke the 

 pelt of a drum stretched across this passage upon a bony 

 rim : of a chain of movable and infinitely curious bones, 

 forming a communication, and the only communication that 

 can be observed, between the membrane last mentioned and 

 the interior channels and recesses of the skull : of cavities 

 similar in shape and form to wind instruments of music, be 

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

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

 the barrel of the ear, as the covering membrane viio'ates, 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 of the body. This assemblage of connected 

 parts constitutes together an apparatus plainly enough rela- 

 tive to the transmission of sound, or of the impulses 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 accus- 

 tomed to call machinery, than any thing I am acquainted 

 with in animal bodies. It seems evidently designed to con- 

 tinue 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 consists of four, which are so disposed, 

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

 drum of the ear, vibrate, all the four are put in motion to- 

 gether ; and, by the result of their action, work the base of 

 that which is the last in the series upon an aperture which 

 it closes, and upon which it plays, and which aperture opens 

 into the tortuous canals that lead to the brain. This last 

 bene of the four is called the stajoes. The office of the drum 

 of the ear is to spread out an extended surface capable of 

 receiving the unpressions of sound, and of being put by ther.i 

 into a state of vibration. The office of the stapes is to re- 

 peat these vibrations. It is a repeating frigate, stationed 



