The posterior wall of the middle ear arises from the mastoid bone and communicates with the mastoid antrum (cavity) through the aditus to antrum.

Mastoid cavity has air cells and is similar to the pockets of such cavities that exist in the skull filled with air and thereby making the skull lighter (air sinuses).

From the posterior wall emerges the tendon of the muscle stapedius which connects to the neck of the stapes bone

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