The inner ear consists of a delicate, complicated fluid-filled tube known as the membranous labyrinth. It lies inside the bony labyrinth, a chamber in the petrous bone of the skull.

The inner ear is separated from the middle ear by two small holes covered by membranes:

• the oval window is partially covered by the base of the stapes and is vibrated when the stapes moves; these vibrations are transmitted to the fluid in the inner ear.
• the round window lies under the oval window and vibrates in the opposite direction to it, allowing the fluid in the inner ear to oscillate freely.