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

ANATOMY OF THE EAR

251

the level of the floor of the aditus and lies in close relation to the posterior
wall.

The lateral wall {Fig. 129) is formed mainly by the tympanic membrane and
the outer bony wall of the epitympanic recess (attic). The medial wall is also
the lateral wall of the internal ear. In it there are two openings (figs. 129, 130,
131), the upper of which is the oval window (fenestra vestibuli) and below it
is the niche leading to the round window (fenestra cochleae), which is closed

6

Fig. 129. Left tympanic cavity as seen from the medial aspect. 1, Epitympanic recess; 2, Body of incus;
3, Chorda tympani; 4, Pyramid; 5, Footplate of stapes; 6, Medial surface of tympanic membrane; 7,
Head of malleus and superior ligament of malleus; 8, Anterior ligament of malleus; 9, Tensor tympani
in its canal; 10, Eustachian tube.

by the secondary tympanic membrane. In front of and between these two
windows lies the promontory. The surface of this bony covering of the basal
coil of the cochlea is grooved for the nerve fibres of the tympanic plexus.
The horizontal portion of the facial nerve is enclosed in a bony canal (the
canal of Fallopius), which is sometimes deficient, and which crosses the
medial wall above the oval window before turning vertically downwards at
the posterior end of the window. The processus cochleariformis, containing
the tendon of the tensor tympani, is situated on the anterior and superior part
of the medial wall in front of the point of entry of the facial nerve from the
inner ear.

The mucosal or epithelial lining of the tympanic cavity is of columnar
ciliated epithelium in that part derived from the tubotympanic recess but in a
posterosuperior direction there is a transition to cuboidal epithelium and
finally to a flattened single layer epithelium lining the mastoid antrum and
air cells.

The ossicles. The three ossicles, clothed in mucosa and supported b>
ligaments, form an articulated connection between the tympanic membrane
and the oval window. The malleus consists of a head, neck, anterior and