. Animal physiology. Physiology, Comparative; Physiology, Comparative. ACTION OF THE TYMPANUM. 391 or slack ; and when in this condition, it vibrates in accordance with grave or deep tones. By the action of a small muscle lodged within the Eustachian tube, it may be tightened, so as to vibrate in accordance with sharper or higher tones; but it will then be less able to receive the impressions of deeper sounds. This state we may artificially produce, by holding the breath and forcing air into the Eustachian tube, so as to make the mem- i e j T. k h g q r f s b Fig. 193.—Vertical Section of the
. Animal physiology. Physiology, Comparative; Physiology, Comparative. ACTION OF THE TYMPANUM. 391 or slack ; and when in this condition, it vibrates in accordance with grave or deep tones. By the action of a small muscle lodged within the Eustachian tube, it may be tightened, so as to vibrate in accordance with sharper or higher tones; but it will then be less able to receive the impressions of deeper sounds. This state we may artificially produce, by holding the breath and forcing air into the Eustachian tube, so as to make the mem- i e j T. k h g q r f s b Fig. 193.—Vertical Section of the Organ op Hearing in Man. The internal portions are enlarged to make them more evident, a, b, c, the external ear; d, entrance to the auditory canal. /; e, e, petrous portion of the temporal bone in which the internal ear is excavated ; g, membrane of the tympanum ; h, cavity of the tympanum, the chain of bones being removed ; i, openings from the cavity into the cells, j, excavated in the bone; on the side opposite the membrana tympani are seen the fenestra ovalis and rotunda: k, Eustachian tube ; I, vestibule ; m, semicir- cular canals ; n, cochlea; o, auditory nerve ; p, canal by which the carotid artery enters the skull; q, part of the glenoid fossa, which receives the head of the lower jaw ; r, styloid process of the temporal bone. brane bulge out by pressure from within ; or by exhausting the cavity, by an effort at inspiration with the mouth and nostrils closed, which will cause the membrane to be pressed inwards by the external air. In either case the hearing is immediately found. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Carpenter, William Benjamin, 1813-1885. London : Wm. S. Orr and Co.
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