Oticon intra aural ('in the ear') hearing aid, model I 11 V, by Oticon, Denmark, 1978-1981.

An intra-aural hearing aid sits in the ear canal rather than externally behind the ear. So successful is the design that it has been copied in recent years for audio earphones. This small hearing aid amplifies sound down the ear canal to the ear drum. This in turn vibrates and passes the sound to the bones of the middle ear, which are called ossicles. These bones vibrate and amplify the sound to pass it to the inner ear, which contains the cochlea. The hairs of the bones in the inner ear send a nerve impulse to the brain.