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The tympanic part of the temporal bone is a curved plate of bone lying below the squama, in front of the mastoid process, and surrounding the external acoustic meatus. It originates as a separate bone (tympanic bone), which in some mammals stays separate through life. In evolution, a portion of it is derived from the angular bone of the reptilian lower jaw. == Surfaces == Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony external acoustic meatus. Medially, it presents a narrow furrow, the ''tympanic sulcus'', for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland. 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「Tympanic part of the temporal bone」の詳細全文を読む スポンサード リンク
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