Page:Philosophical Transactions - Volume 003.djvu/42

 the passage of his left Ear was quite shut up, and that of the right Ear proportionally distended, and too open. This Gentleman being for some time recommended to my Care, amongst other things, I spent some thoughts in searching the cause of his Deafness in the Ear, whose passage was open. And having found, that the Auditory Nerve was not perished, but that he could hear the sound of a Lute-string, holding one end thereof in his Teeth; and had some perception of any very vehement sound, I supposed the defect to lie in the want of due Tension of the Tympanum of his Ear; whose use I took to be, onely to preserve the Auditory Nerve, and Brain, and inward parts of the Ear from outward injury by cold, Dull, &c and to be no more to Hearing, than glass in the window is in a Room to seeing, i.e. as the one intromits Light without Cold or offence to those in the room, so the other permits Sound to pass, and shuts out what else might offend the Organ; as appears in the Experiment of breaking the Tympanum of a Dog, who hears never the worse for some few weeks, till other causes, as Cold, &c, vitiate the Organ.

But for the Free passage of the Sound into the Ear, it is requisite, that the Tympanum be tense and hard stretched; otherwise the laxness of that membrane will certainly dead and damp the Sound. And because the Tympanum is fixed in the circumference thereof to the Annulus Osseus, and so is not capable of Tension that way, in such manner as a Drum is braced; there remains another way, by drawing it at the Center into a Conoid form. And that is the principal office of the 3. Ossicles, viz, the Malleus, Incus, and Stapes; whereof the Stapes is fixt to the inner Bone, and part of the Malleus, to the Tympanum, and the Incus between them joyn'd on one part to the Malleus, and on the other to the Stapes: by Ginglymoide Joynts, such as in which the upper and lower double Teeth meet one another. And by the help of a Muscle drawing the Incus, these three bones, which otherwise could lye more streight, are brought to a Curved or Arched posture; and the Stapes being fixt unmovable, the Malleus yields, to bring the terms of that line nearer, in proportion as it is curved, and draws the Center of the Tympanum, stretching the surface of it from a Plain to a Conoid figure, within the same Rh