An American text-book of physiology . n front of the ear, though the contrary statement is frequently erroneouslymade. When the sound of the fork held between the teeth has failed, it mayagain be heard by stopping the ears. The Internal Ear, or Labyrinth.—The internal ear is the site of the trueorgan of hearing. The membranous labyrinth (PI. 2, Fig. 4; Fig. 278) is a com-plicated system of membranous tubes and sacs, in which terminate at particularpoints the filaments of the auditoiy nerve; it is contained within a chamber,the bony labyrinth, hollowed out in the petrous bone. The cavity of the
An American text-book of physiology . n front of the ear, though the contrary statement is frequently erroneouslymade. When the sound of the fork held between the teeth has failed, it mayagain be heard by stopping the ears. The Internal Ear, or Labyrinth.—The internal ear is the site of the trueorgan of hearing. The membranous labyrinth (PI. 2, Fig. 4; Fig. 278) is a com-plicated system of membranous tubes and sacs, in which terminate at particularpoints the filaments of the auditoiy nerve; it is contained within a chamber,the bony labyrinth, hollowed out in the petrous bone. The cavity of the bony 81(5 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. lal)yrintli( 275, 270) consists of a median part, the vestibule, which is pro-lougtd posteriorly in the system of semicircular canals and anteriorly in thecochlea. The vestibule is a space which measures about one-fifth of an inchin diameter, and it is perforated in its outer wall by an oval opening knownas the Jenesira ovalis. The semicircular canals are three tubes of ciroular. Fig. 275.—Right bony labyrinth, viewed fromouter side : the figure represents the appearanceproduced by removing the petrous bone down totlie denser layer immediately surrounding thelabyrinth (from Quain, after Sommering): 1, 2,3,the superior, posterior, and horizontal semicir-cular canals; 4, 5, 6, the ampullae of the same;7, the vestibule; 8, the fenestra ovalis; 9, fenestrarotunda ; 10, first turn of the cochlea; 11, secondturn; 12, apex. Fig. 276.—Interior view of left bony labyrinth afterremoval of the superior and external walls (fromQuain, after Sommering): 1, 2, 3, the superior, pos-terior, and horizontal semicircular canals; 4, foveahemi-elliptica; o, fovea hemisphcrica; 6, commonopening of the superior and jioRterior semicircularcanals ; 7, opening of the aqueduct of the vestibule ;8, opening of the aqueduct of tlie cochlea; 9, thescala vestibuli; 10, scala tympani; the lamina spiralisseparating 9 and 10. section, known respectively
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