. Animal biology. Zoology; Biology. SUBPHYLUM VERTEBRATA 337 includes one chamber known as the sacculus, in connection with which is the organ of hearing, and another known as the utriculus, in connection with which is the organ of equihbrium. The two cavities—sacculus and utriculus—communicate with one another through the endolymphatic duct, and each has a potential opening into the middle ear. The sacculus is the ventrally situated chamber. In connection with it is a spirally coiled canal known as the cochlea (Fig. 235). In the canal of the cochlea is a sheet of sensory cells known as the or
. Animal biology. Zoology; Biology. SUBPHYLUM VERTEBRATA 337 includes one chamber known as the sacculus, in connection with which is the organ of hearing, and another known as the utriculus, in connection with which is the organ of equihbrium. The two cavities—sacculus and utriculus—communicate with one another through the endolymphatic duct, and each has a potential opening into the middle ear. The sacculus is the ventrally situated chamber. In connection with it is a spirally coiled canal known as the cochlea (Fig. 235). In the canal of the cochlea is a sheet of sensory cells known as the organ of Corti, which is the essential organ of hearing. Sound waves stimulating these cells mechanically give rise to impulses which, transmitted by the auditory nerve, are interpreted by the brain as sensations of sound. In connec- tion with the utriculus, which is the more dorsal chamber, are three semi- circular canals lying in three planes. At the end of each of these canals Sccf/cr vesfibuli Vestibular J^^^^^ "'^m ..,^^^^^^^°"^ membrane-. Oangilor, ^^^l^~-^cociilear nerve Fig. 235.—Section of the cochlea showing the two scalae, which communicate at the tip of the coils, and the essential organ of hearing, the organ of Corti, lying in a part of the Bcala vestibuli separated from the rest by a thin membrane, called the vestibular mem- brane, or membrane of Reissner. The mass of bone surrounding the cochlea is shown cut away from the rest of the temporal bone, in which the whole auditory organ is contained. is a dilatation known as an ampulla, in which are sensory hairs which, when the body is moved, are stimulated by waves of movement in the lymph and give a sense of position or of equilibrium. The opening from the utriculus into the middle ear, known as the fenestra ovalis, is closed by the innermost of three bones known as the stapes, while the opening from the sacculus into the middle ear, the fenestra rotunda, is closed by a thin membrane. The middle ear
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Keywords: ., bookcentury1900, bookcoll, booksubjectbiology, booksubjectzoology
