The Internal Ear.—"The labyrinth consists primarily of chambers and tubes hollowed out in the temporal bone and inclosed by it on all sides, except for the oval and round foramens on its exterior, and certain apertures for blood-vessels and the auditory nerve; during life all these are closed water-tight in one way or another. Lying in the bony labyrinth thus constituted are membranous parts, of the same general form but smaller, so that between the two a space is left; this is filled with a watery fluid, called the perilymph; and the membranous internal ear is filled by a similar liquid, the endolymph.
Fig. 19.—Casts of the bony labyrinth. A, left labyrinth seen from the outer side; B, right labyrinth from the inner side; C, left labyrinth from above; Co, cochlea; V, vestibule; Fc, round foramen; Fv, oval foramen; h, horizontal semicircular canal; ha, its ampulla; vaa, ampulla of anterior vertical semicircular canal; vpa, ampulla of posterior vertical semicircular canal; vc, conjoined portion of the two vertical canals.
The Bony Labyrinth.—"The bony labyrinth is described in three portions, the vestibule, the semicircular canals, and the cochlea; casts of its interior are represented from different aspects in [Fig. 19.] The vestibule is the central part and has on its exterior the oval foramen (Fv) into which the base of the stirrup-bone fits. Behind the vestibule are three bony semicircular canals, communicating with the back of the vestibule at each end, and dilated near one end to form an ampulla. The bony cochlea is a tube coiled on itself somewhat like a snail's shell, and lying in front of the vestibule.
The Membranous Labyrinth.—"The membranous vestibule, lying in the bony, consists of two sacs communicating by a narrow aperture. The posterior is called the utriculus, and into it the membranous semicircular canals open. The anterior, called the sacculus, communicates by a tube with the membranous cochlea. The membranous semicircular canals much resemble the bony, and each has
Fig. 20.—A section through the cochlea in the line of its axis.