File:The cat - an introduction to the study of backboned animals, especially mammals (1881) (19964189814).jpg

Title: The cat : an introduction to the study of backboned animals, especially mammals
Identifier: catintroduction00miva (find matches)
Year: 1881 (1880s)
Authors: Mivart, St. George Jackson, 1827-1900
Subjects: Cats; Anatomy, Comparative
Publisher: New York : Scribner's
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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chap, ix.) NERVOUS SYSTEM AND ORGANS OF SENSE. 303 continuous with the cells hearing hair-like processes, which have been described as lying beside the rods of the organ of Corti. Thus here again—as in the organs of sight, smell, and taste—the ultimate structure which ministers to special sense is a system of rod-like filaments proceeding from spheroidal cells. Apart from the special, function of the ear—hearing—the various accessory structures serve the following purposes in aiding that function: the pinna serves to collect the sonorous waves, by its prominences and ex-» cavations, and to direct them towards the aperture of the meatus externus. This collecting process is greatly aided by the muscles, which enable the pinna to be turned in various directions. At the bottom of the meatus, the sonorous waves act upon the tympanic membrane, the vibrations of which are conveyed by the auditory ossicles across the tym- panum to the fenestra ovalis and so to the perilymph, and, finally, through the walls of the membranous labyrinth, to the hair-like processes projecting into the endolymph of the ampulla?, and to those of the organ of Corti. The vibrations of the rods of the last named organ doubtless intensify the vibratory action, as do the otoliths enclosed within the utricle and sacculus. The Eustachian tube places the air inside the tympanum in communication with the exterior, and so prevents undue tension. The stapedius and tensor tyrupani muscles tend by their contraction to tighten the tympanic membrane and that of the fenestra ovalis, and so to moderate the effect of too great sound. Thus the labyrinth, with its fluid con- tents, can be affected either by aerial waves through the meatus, tympanum, and fenestra ovalis, or through the bones and solid structure of the head. § 27. Certain marked analogies exist between the ear and the eye, with certain noteworthy differences. Both are protected by skull bones, but the ear much more completely so. Both are protected by external folds of integuments furnished with muscles—the pinna and the eyelids. Both are supplied by a nerve of special sense, which enters
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Fig. 140.—Diagram of the Audi- tory Epithelium assd the mode of termination of the Xerves of the ampull.e. c. Columnar epithelium. sp. Spindle-shaped cells, each support- ing an* auditory hair, h. b. Basal supporting cells. n. Two nerve-fibres, passing through the layer of membrane (called the tunica propria) immediately be- neath the epithelium, to join the plexus in the epithelium. I. Limit of the membrane beneath the epithelium.

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