||The roof of the tympanic cavity,the tegmen tympani, separates the tympanic cavity from the contents of the middle cranial fossa (the meninges and overlying temporal lobe of the brain).
The posterior wall of the box features a depression which contains the short process of the incus (the fossa incudis) and admits the chorda tympani nerve into the middle ear space.
Posterosuperiorly the mastoid antrum connects the tympanic cavity to the mastoid air cell system.
The stapedius muscle arises from a small pyramidal eminence situated at the junction of the posterior and medial walls.
The medial wall of the middle ear is also the lateral aspect of the inner ear. The most prominent landmark is an outward bulge (the promontory) which covers the basal turn of the cochlea and encroaches into the middle ear space to within 2 mm of the tympanic membrane.
There are two apertures in the medial wall of the middle ear which communicate with the inner ear: the oval window which is occupied by the stapes footplate, and the round window which is covered by a thin membrane (the round window membrane).