The mastoid bone is a prominent bony structure located behind the ear. It is part of the temporal bone of the skull and contains air-filled spaces called mastoid cells, which help with sound transmission and balance. The mastoid bone is important for protecting the inner ear and supporting the surrounding structures. In addition to its protective role, the mastoid bone serves as an attachment point for several muscles, including those involved in head movement. Infections in the middle ear can sometimes spread to the mastoid bone, leading to a condition known as mastoiditis, which may require medical treatment.