The inner ear, containing the essential parts of the organ of hearing. It consists of two labyrinthine compartments. The bony labyrinth is a complex of three interconnecting cavities or spaces (semicircular canal; vestibule; and cochlea) in the temporal bone. Within the bony labyrinth, lies the membranous labyrinth which is a complex of sacs and tubules (saccule and utricle; cochleaR DUCT) forming a continuous space enclosed by epithelium and connective tissue. These spaces are filled with labyrinthine fluids of various compositions. [MeSH]