Coloured 3D computed tomography (CT) scan of the outer and middle components of a healthy adult right ear. The outer ear's pinna (centre) is the external part of the ear. Leading from the pinna to the middle ear is the external auditory canal. Surrounding the auditory canal are mastoid air cells that provide protection and regulate air pressure. The pointed structure at upper right is the Eustachian tube, a passageway that connects the middle ear to the throat.