 The cortilymphatic space lies within the organ of Corti. It is a true intercellular space. The cells surrounding the space loosely resemble an absorptive epithelium. The cortilymphatic space is filled with cortilymph, which has a composition similar to that of extracellular ﬂuid.
Structures of the Bony Labyrinth
The bony labyrinth consists of three connected spaces within the temporal bone.
The three spaces of the bony labyrinth, as illustrated in Figure 25.7, are the:
FIGURE 25.6 • Photograph of the three articulated human auditory ossicles. The three ossicles are the malleus, the incus, and the stapes. 30.
The vestibule is the central space that contains the utricle and saccule of the membranous labyrinth.
The vestibule is the small oval chamber located in the center of the bony labyrinth. The utricle and saccule of the membranous labyrinth lie in elliptical and spherical recesses, respectively. The semicircular canals extend from the vestibule posteriorly, and the cochlea extends from the vestibule anteriorly. The oval window into which the footplate of the stapes inserts lies in the lateral wall of the vestibule.
The semicircular canals are tubes within the temporal bone that lie at right angles to each other.
Three semicircular canals, each forming about three quarters of a circle, extend from the wall of the vestibule and return to it. The semicircular canals are identified as anterior, posterior, and lateral and lie within the temporal bone at approximately right angles to each other. They occupy three planes in space— sagittal, frontal, and horizontal. The end of each semicircular canal closest to the vestibule is expanded to form the ampulla (Fig. 25.8a). The three canals open into the vestibule through five orifices; the anterior and posterior semicircular canals join at one end to form the common bony limb (see Fig. 25.8a).
The cochlea is a cone-shaped helix connected to the vestibule.
The lumen of the cochlea, like that of the semicircular canals, is continuous with that of the vestibule. It connects to the vestibule on the side opposite the semicircular canals. Between its base and the apex, the cochlea makes about 2.75 turns around a central core of spongy bone called the modiolus (Plate 108, page 946). A sensory ganglion, the spiral ganglion, lies in the modiolus. A thin membrane (the secondary tympanic membrane) covers one opening of the canal, the round window on its inferior surface near the base.
Structures of the Membranous Labyrinth
The membranous labyrinth contains the endolymph and is suspended within the bony labyrinth.
The membranous labyrinth consists of a series of communicating sacs and ducts containing endolymph. It is  FOLDER 25.1 Clinical Correlation: Otosclerosis