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The round window is one of the two openings from the middle ear into the inner ear. It is sealed by the round window membrane, which vibrates with opposite phase to vibrations entering the inner ear through the oval window. It allows fluid in the cochlea to move, which in turn ensures that hair cells of the basilar membrane will be stimulated and that audition will occur. ==Structure== The round window is situated below and a little behind the oval window, from which it is separated by a rounded elevation, the promontory. It is placed at the bottom of a funnel-shaped depression (the round window niche) and, in the macerated bone, opens into the cochlea of the internal ear; in the fresh state it is closed by a membrane, the secondary tympanic membrane or round window membrane, which is a complex saddle point shape. The visible central portion is concave toward the tympanic cavity and convex toward the cochlea but towards the edges, where it is hidden in the round window niche, it curves the other way. This membrane consists of three layers: * an external, or mucous, derived from the mucous lining of the tympanic cavity; * an internal, from the lining membrane of the cochlea; * and an intermediate, or fibrous layer. Both the oval and round windows are about the same size, approximately 2.5 mm2. The entrance to the round window niche is often much smaller than this. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「round window」の詳細全文を読む スポンサード リンク
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