Middle ear

The middle ear (auris media) includes a lining mucosa and an air-filled drum cavity (about 1 cm ^{3 in} volume ) and an auditory (Eustachian) tube. The cavity of the middle ear communicates with the mastoid cave and through it with mastoid cells located in the thickness of the mastoid process.

The drum cavity (cavitas tympanica, s. Cavum thympani) is located in the thickness of the pyramid of the temporal bone, between the external auditory passage laterally and the bone labyrinth of the inner ear medially. In the cavity there are 6 walls, and in its form it is compared with a tambourine, placed on the rib and inclined to the outside.

1. The upper covering wall (paries tegmentalis) is formed by a thin plate of bone substance (the roof of the tympanum, tegmen tympani) separating the drum cavity from the cranial cavity.
2. The lower jugular wall (paries jugularis) corresponds to the bottom wall of the pyramid in the place where the jugular fossa is located.
3. The medial labyrinth wall (paries labyrinthicus) is complicated, separating the drum cavity from the bone labyrinth of the inner ear. On this wall there is a promontory (promontorium) projecting towards the drum cavity. Above the headland and somewhat posteriorly there is an oval window of the vestibule (fenestra vesitibuli) leading on the threshold of the bone labyrinth; it is covered by the base of the stirrup. Somewhat higher than the oval window and behind it is the transverse projection of the wall of the canal of the facial nerve - the protrusion of the facial canal (prominentia canalis facialis). Behind and below the cape is a window of the cochlea (fenestra cochleae), closed by the secondary eardrum (membrana tympani secundaria). This membrane separates the drum cavity from the tympanic staircase.
4. The posterior mastoid wall (paries mastoideus) in the lower part has a pyramidal elevation (eminentia pyramidalis), inside which the stenosis (m. Stapedius) begins. In the upper part of the posterior wall the tympanic cavity continues into the mastoid cave (antrum mastoideum), into which the mastoid cells of the eponymous process also open.
5. The front carotid (paries caroticus), the lower part of it, separates the tympanum from the carotid canal, in which the internal carotid artery passes. In the upper part of the wall there is an opening of the auditory tube, which connects the drum cavity with the nasopharynx.
6. The lateral membranous wall (paries membranaceus) is formed by the tympanic membrane and the surrounding parts of the temporal bone.

In the tympanic cavity there are three auditory ossicles covered with mucous membrane, as well as ligaments and muscles.

The auditory ossicula auditus, s. Auditoria, miniature in size, joining together, constitute a chain that extends from the tympanic membrane to the window of the vestibule opening into the inner ear. In accordance with its shape, the bones were given the following names: a hammer, an anvil, a stirrup . The malleus has a round head (caput mallei), which passes into the long handle of the malleus (manubrium mallei) with two processes: lateral and anterior (processus lateralis et anterior). The anvil (incus) consists of a body (corpus incudis) with an articular fossa for articulation with the head of the malleus and two legs: a short (crus breve) and a long (crus longum) with a thickening at the end. Thickening on a long leg - a lenticular process (processus lenticularis) serves to connect the head of the stirrup. The stapes have a head (caput stapedis), two legs - anterior and posterior (crus anterius and posterius), connected with the base of stapes (basis stapedis).

The hammer with its handle along its entire length is spliced with the tympanic membrane so that the end of the handle corresponds to the navel on the outside of the membrane. The head of the malleus with the help of the joint connects with the body of the anvil and forms an anvil-hammer joint (articulatio incudomallearis). The anvil, in turn, is connected with the head of the stapes by a lenticular process, forming an anvil-stern joint (articulatio incudostapedia). The joints are strengthened with miniature ligaments.

With the aid of a mobile chain in the joints consisting of three auditory ossicles, the oscillations of the tympanic membrane resulting from the action of a sound wave on it are transmitted to the window of the vestibule in which the base of the stapes is movably fixed by means of a ring ligament of the stapes (lig. Anulare stapedis). Regulate the movements of the bones and protect them from excessive fluctuations with strong sound, two muscles attached to the auditory ossicles. The muscle that strains the eardrum (M. Tensor tympani) lies in the same half-channel of the musculoskeletal canal, and its thin and long tendon is attached to the initial part of the hammer handle. This muscle, tightening the handle of the malleus, strains the eardrum. The staped muscle (m. Stapedius) begins on a pyramidal elevation and a thin tendon attaches to the posterior stalk of the stapes, near its head. With the contraction of the stenosis, the pressure of the base of the stapes inserted into the window of the vestibule is weakened.

[1], [2], [3], [4], [5]