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Full text of "Diseases Of The Nose Throat And Ear"

ANATOMY OF THE EAR

259

called the periotic capsule and this in turn changes to dense bone in which
some cartilage cells persist throughout life. This dense enchondral bone
forms the bony labyrinth embedded, fossil-like, in the petrous temporal bone.
The interior of the bony labyrinth is lined by endosteum. The central part of
the bony labyrinth is the vestibule in the lateral wall of which lies the fenestra
vestibuli (oval window) closed by the footplate of the stapes and the annular
ligament. The medial or inner wall of the vestibule is directed towards the
internal acoustic meatus and is perforated by nerve endings. It contains two
depressions—the spherical recess for the saccule and the elliptical recess for
the utricle. Below the elliptical recess there is the small opening of the
aqueduct of the vestibule which transmits the endolymphatic duct. The
posterior, superior and inferior walls of the vestibule contain the five openings
of the semicircular canals. The lateral or horizontal canal has an opening at
each end but the superior and posterior vertical canals have a common
opening at their non-ampullated ends, the crus commune (Figs. 139, 140).

The bony cochlea, anterior to the vestibule, is a spiral tube wound two and
a half times round its central axis or modiolus. Its base is directed towards the

fig. 142. Vertical coronal section through right
ear, axial section through cochlea. 1, Tensor
tympani; 2, Helicotrema; 3, Canal for greater
superficial petrosal nerve; 4, Modiolus; 5,
Facial nerve; 6, Cochlear aqueduct; 7, Edge of
; 8, Carotid

,

-bone capsule of cochlea
canal; 9, Tubal cells; 10, Tuba! part of tym-
panic cavity.

internal acoustic meatus and its apex towards the internal carotid artery
(Fig. 142). From the modiolus, which contains the cochlear nerve, a hollow
bony ledge (spiral lamina) projects into the lumen of the tube transmitting
the branches of the nerve. This ledge commences in the vestibule just above
the fenestra cochleae (round window) and ends near the apex of the cochlea
at the hamulus or hook. The basilar membrane of the membranous cochlea
is attached to the edge of the bony spiral lamina and the outer surface of the
membranous cochlea is attached to the inner wall of the bony cochlea thus
dividing each coil of the bony cochlea into three parts: (1) the upper part,
the scala vestibuli, commences from an opening in the vestibule below the
spherical recess, (2) the lower part, the scala tympani, begins at the fenestra
cochleae (round window), (3) the membranous cochlea lying between the
upper and lower parts is in effect part of the scala vestibuli separated from
it by a membrane (Reissner's membrane) and is known also as the scala
media. At the apex ofthe cochlea the membranous cochlea ends blindly and
in this region, known as the helicotrema (Figs. 140, 142 and 143), the scala
vestibuli and scala tympani are continuous with one another.