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.