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

ANATOMY OF THE EAR

253

with the head of the stapes. The stapes, suitably named from its stirrup-
shaped appearance, has a head, a neck, two crura or limbs, and a footplate
which is fixed to the margins of the oval window by an annular ligament.

The tympanic muscles are stimulated by sound. The tensor tympani arises
from the cartilaginous part of the auditory tube, from the adjacent part of the
great wing of the sphenoid and from the bony canal in which it lies. Its tendon
bends laterally around the processus cochleariformis and is inserted into the
medial edge and anterior surface of the handle of the malleus. The nerve
supply is from the motor division of the trigeminal nerve through the otic
ganglion, and its action is to tense the tympanic membrane by drawing it
medially. The tendon of the stapedius muscle, after emerging from the
pyramid, is inserted into the neck of the stapes. It has an action of damping
the movement of the stapes by tilting outwards the anterior end of the foot-
plate, and it is supplied by the facial nerve.

Tympanic ligaments and spaces. The anterior and posterior ligaments of
the malleus surround the neck and jointly form the axis ligament attached to
the anterior and posterior ends of the tympanic notch. From the head of the
malleus and the body of the incus a superior ligament suspends each from
the roof of the attic. The posterior ligament of the incus attaches the short
process of the incus to the fossa incudis in the aditus, and the annular liga-
ment attaches the footplate of the stapes to the margins of the oval window.
The folds of mucous membrane around the ossicles and ligaments form spaces
or pouches in which local suppuration may occur. These spaces are related
to the drumhead and are situated below the level of the lateral ligaments of
the malleus. They are the anterior and posterior spaces of the drumhead and
Prussak's space {Fig. 132). These well-defined intercommunicating spaces are
present in the attic, the upper portion of the lateral space opening into the
aditus. On the medial wail of the latter lies the rounded prominence of the
bony wall of the lateral semicircular canal.

Tympanic vessels and nerves. The cavity is well supplied by branches arising
from the maxillary, stylomastoid, middle meningeal, ascending pharyngeal
and internal carotid arteries. The veins drain into the pterygoid plexus and

Fig. 132. Vertical coronal section through
right ear, showing canals. 1, Epitympanic
recess; 2, Head of malleus; 3, Facial nerve;
4, Two ends of lateral canal; 5, Superior canal;
6, Remains of fossa subarcuata in labyrinth.
nucleus; 7, Ductus endolymphaticus; 8, Two
ends of posterior canal; 9, Jugular bulb; 10,
Hypotympanum; 11, External meatus; 12,
Tympanic membrane; 13, Stapes; 14,
Prussak's space.