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Untitled Article
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Note: This text has been automatically extracted via Optical Character Recognition (OCR) software. The text has not been manually corrected and should not be relied on to be an accurate representation of the item.
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Untitled Article
taineil fluid . The distribution of the auditory nerve on the cochlea is parti cularly beautiful . The aqueducts of the ear are two very fine tubes , passing from the vestibulum and cochlea to open on the surface of that part of the brain called the dura mater .
From this account of the structure of the ear , it will appear that the organ is no less artificially and mechanically adapted to its office than the eve . Its general form is evidently adapted to the reception of sound , that
js , knowing that what we denominate sound consists of pulses of the air , we perceive , in the structure of the ear , a suitableness to receive impressions from this species of action , and to propagate these impressions to the brain . The external ear , as we
have seen , is calculated , like a trumpet used by the dea £ to catch , collect and convey onwards , the pulses just mentioned : it consists of a tube which leads into the head , lying at the root of this outward ear ; of a thin membrane like a drum-head , stretched
across this passage upon a bony rim ; of a chain of rnoveable and highlycurious bones , forming a communication between the membrane and the interior canals and recesses of the
skull ; of cavities , similar in shape and form to wind instruments of music , being either spiral or portions of circles ; of the Eustachian tube , like the hole of a drum , to let the air pass freely into and out of the barrel of the
ear , either as the membrane vibrates , or as the temperature may be changed ; and the whole labyrinth is wrought > nto the substance of the hardest bone tfthe body . The communication within , formed ty the ossicula , or small bones of the
car , is perfectly mechanical , and seems evi dently designed to continue towards the sensorium the tremulous Motio ns which are excited in the n nabrane of the tympanum or drum « the ear . The compares of the tones are so disposed and so hinge ** P ° a oue another , as that , if the membrane
ofthe drum of the ear vibrate , * ' the four are put in motion toge-^ r > and by the result of their action * ° nt upon the base of that which is t e test in the series , upon an aperj re > vkich it closes , and upon which Pteys , which aperture opens intft br" " ^ . CiMlaIs that lead to the air *« This ; Just bone its-the s tapes .
Untitled Article
The office of the drum of the ear is to spread out an extended surface capable of receiving the impressions of sound , and of being put by them into a state of Vibration . The business of
the stapes is to repeat these vibrations . Hence it may be understood how the sensation of sound is excited , by any thing which communicates a vibratory motion to the stapes , though not , as in ordinary cases , through the intervention of the membrana
tvmpani . This may be 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 a tremulous body . It appears to be done , likewise , by the ear itself , even when this membrane ,
the drum of the ear , is greatly damaged ; so that either in the natural or preternatural state of the organ , the use of the chain of bones is , no doubt , to propagate the impulse in a direction towards the brain , and to propagate it with the advantage of
a lever . This mechanical advantage consists in increasing the force and strength of the vibration , and at the same time diminishing the space through which it oscillates : both these changes may augment or facilitate the still deeper action o ^ the au ditory nerves .
The advantage of the Eustachian tube may , as we have seen , be made put upon known pneumatic principles , being- intended to bring a supply of air , when wanted , into the cavity called the tympanum ; which cavity could not have answered the end
required had it been left as a vacuum , or filled with an aqueous fluid , or been occupied with confined air . The membrana tympani is not found in the ears of fishes , which . Mrnishes an additional proof of what indeed is indicated b } ' every thing about it , that it is appropriated to the action of air , or of an elastic medium .
It bears , as we have seen , a resemblance to the head of a drum in this , that its use depends upon its tension . In the drum the skin is carried over a hoop , and braced as occasion requires , by means of strings attached to its circumference . In the ear the same
purpose is provided for , more simply , by a different expedient , viz * by the handle-end of the malleus pressing upon its centre . To demonstrate tiie wisdom of the
Untitled Article
Natural Theology . No . V . — The Ear . SOS
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), May 2, 1815, page 303, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct1760/page/39/
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