Posterior wall lies close to the mastoid air cells & presents the features from above downwards.
1) Aditus: Superiorly, an opening through which attic communicates with antrum.
2) Fossa incudes: A depression, lodges short process if Incus.
3) Pyramid: a bony projection through the summit of which appears the tendon of stapedius muscle to get attachment to the neck of Stapes.
4) Facial recess: A depression lateral to the pyramid. It is bounded by-
Medially: vertical part of facial nerve.
Laterally: Chorda tympani.
Above: Fossa incudes.
SURGICAL IMPORTANCE: Direct access can be made through this into middle ear without disturbing posterior canal wall.
RELATION OF FACIAL NERVE IN THE ABOVE WALL: The vertical portion of facial nerve courses down the posterior wall lateral to the pyramid to its exit in the Stylomastoid foramen.
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