Malleus
The malleus is so called because it resembles a hammer.
It is the largest, and the most laterally placed ossicle.
It has the following parts:
1. The rounded head lies in the epitympanic recess.
It articulates posteriorly with the body of the incus.
It provides attachment to the superior and lateral ligaments
2. The neck lies against the pars flaccida and is related medially to the chorda tympani nerve.
3. The anterior process is connected to the petrotympanic fissure by the anterior ligament.
4. The lateral process projects from the upper end of the handle and provides attachment to the malleolar folds.
5. The handle extends downwards, backwards and medially, and is attached to the upper half of the tympanic membrane.
lncus or Anvil
It is so called because it resembles an anvil, used by blacksmiths.
It resembles a molar tooth and has the following parts:
1. The body is large and bears an articular surface that is directed forwards.
It articulates with the head of the malleus.
2. The long process projects downwards just behind and parallel with the handle of the malleus. Its tip bears a lentiform nodule directed medially which articulates with the head of the stapes
Stapes
- This bone is so called because it is shaped like a stirrup.
- It is the smallest, and the most medially placed ossicle of the ear.
It has the following parts:
a. The small head has a concave facet which
articulates with the lentiform nodule of the incus.
b. The narrow neck provides insertion, posteriorly,
to the thin tendon of the stapedius.
c. Two limbs or crura;
anterior, the shorter and less curved; and
posterior, the longer which diverge from the neck and are attached to the footplate.
d. The footplate, a footpiece or base, is oval in shape,
and fits into the fenestra vestibuli.
Joints of the Ossicles
1. The incudomalleolar joint is a saddle joint.
2 The incudostapedial joint is a ball and socket joint.
- Both of them are synovial joints.
- They are surrounded by capsular ligaments.
- Accessory ligaments are three for the malleus, and one each for the incus and the stapes which stabilize the ossicles.
- All ligaments are extremely elastic
Muscles of Middle ear
- There are two muscles, the tensor tympani and the stapedius.
- Both act simultaneously to damp down the intensity of high-pitched sound waves and thus protect the internal ear.
- The tensor tympani lies in a bony canal that opens at its lateral end on the anterior wall of the middle ear, and at the medial end on the base of the skull.
- The auditory tube lies just below this canal.
- The muscle arises from the walls of the canal in which it lies. Some fibres arise from the cartilaginous part of the auditory tube, and some from the base of the skull.
- The muscle ends in a tendon which reaches the medial wall of the middle ear and bends sharply around the processus cochleariformis.
- It then passes laterally across the tympanic cavity to be inserted into the handle of the malleus.
- The tensor tympani is supplied by the mandibular nerve.
- The fibres pass through the nerve to the medial pterygoid, and through the otic ganglion, without any relay.
- It develops from the mesoderm of first branchial arch.
- The stapedius lies in a bony canal that is related to the posterior wall of the middle ear.
- Posteriorly, and below, this canal is continuous with the vertical part of the canal for the facial nerve.
- Anteriorly, the canal opens on the summit of the pyramid.
- The muscle arises from the walls of this canal.
- Its tendon emerges through the pyramid and Passes forwards to be inserted into the posterior surface of the neck of the stapes.
- The stapedius is supplied by the facial nerve.
- It develops from the mesoderm of the second branchial arch.
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