Located in the middle third of the petrous pyramid, the inner ear comprises the bony labyrinth, which contains the auditory organ with the cochlea to the front or conical chamber and the balance organ, comprising the semi-circular canals and the vestibule to the back.
This bony chamber is filled with a liquid, the perilymph, which protects the membranous labyrinth.

The membranous labyrinth follows the contours of the bony labyrinth and divides into two parts:
the front part, or cochlear duct, and the back part comprising the utricle, the saccule and the semicircular canals.
It forms a group of vesicles and ducts containing endolymph.