The facial nerve comes through the middle ear on its way to the muscles
of facial expression.
It is enclosed in a bony canal upon the inner wall of the tympanic
cavity and extends backward and downward to emerge below the ear.
Within the ear, it gives off a branch called the chorda tympani, a
name derived from the fact that it clings to the inner surface of
the tympanic membrane.
This nerve goes forward and downward under the lower jaw, where it
gives off branches to the taste buds and tongue.
Mastoid Structure.
Just behind the tympanic cavity is a complex cluster of air-conditioning
cavities or cells, of which the partitions constitute the spongelike
structure of the mastoid process of the temporal bone.
These mastoid cells communicate with a central space, which is called
the mastoid antrum. The mastoid antrum, in turn, communicates with
the tympanic cavity.