Fig. (9) Schematic of the 5 boney canals radiating out from the vestibulo-otic labyrinth. The internal auditory canal (IAC) is invested with a thin dural lining. The external auditory canal (EAC) is invested with a typically thin lining of skin. Vestibular aqueduct (VA) lining is variable. The endolymphatic sac (ELS) is more invested with vascularized tissue. The cochlear aqueduct (CA) is lined with periosteum. The eustachian tube (ET) is musculocartilagenous in its nasopharyngeal portion, and the middle ear (me) and mastoid (m) have a thin lining of respiratory mucosa.