28 
APPLICATION OF THE ARGUMENT. 
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 cavites, sim¬ 
ilar in shape and form to wind instruments 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 of 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 anything 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 consists of four, which are so dis¬ 
posed, and so hinge upon one another, as that if the mem¬ 
brane, the drum of the ear, vibrate, all the four 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 
aperture which it closes, and upon which it plays, and 
which aperture opens into the tortuous canals that lead to 
the brain. This last bone of the four is called the slopes. 
The office of the drum of the ear is to spread out an ex¬ 
tended surface, capable of receiving the impressions of 
sound, and of being put by them into a state of vibration. 
The office of the stapes is to repeat these vibrations. It is 
a repeating frigate, stationed more within the line. From 
which account of its action may be understood, how the 
sensation of sound will be excited by anything which 
communicates a vibratory motion to the stapes, though not, 
as in all ordinary cases, through the intervention of the 
membrana tympani. This is done by solid bodies applied 
to the bones of the skull, as by a metal bar held at one 
end between the teeth, and touching at the other end a 
tremulous body. It likewise appears to be done, in a con¬ 
siderable degree, by the air itself, even when this mem¬ 
brane, the drum of the ear, is greatly damaged. Either 
in the natural or preternatural state of the organ, the use 
of the chain of bones is to propagate the impulse in a di 
