The Labyrinthic or Medial Wall
The Labyrinthic or Medial Wall (paries labyrinthica; inner wall) (913) is vertical in direction, and presents for examination the fenestræ vestibuli and cochleæ, the promontory, and the prominence of the facial canal.
The fenestra vestibuli (fenestra ovalis) is a reniform opening leading from the tympanic cavity into the vestibule of the internal ear; its long diameter is horizontal, and its convex border is upward. In the recent state it is occupied by the base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen.
The fenestra cochleæ (fenestra rotunda) is situated below and a little behind the fenestra vestibuli, from which it is separated by a rounded elevation, the promontory. It is placed at the bottom of a funnel-shaped depression and, in the macerated bone, leads into the cochlea of the internal ear; in the fresh state it is closed by a membrane, the secondary tympanic membrane, which is concave toward the tympanic cavity, convex toward the cochlea. 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.Поділитися цим: