The pharyngotympanic tube connects the middle ear with the nasopharynx (Fig. 8.122) and equalizes pressure on both sides of the tympanic membrane. Its opening in the middle ear is on the anterior wall, and from here it extends forward, medially, and downward to enter the nasopharynx just posterior to the inferior meatus of the nasal cavity. It consists of: a bony part (the one-third nearest the middle ear); and a cartilaginous part (the remaining two-thirds).
The opening of the bony part is clearly visible on the inferior surface of the skull at the junction of the squamous and petrous parts of the temporal bone immediately posterior to the foramen ovale and foramen spinosum.
The arterial supply to the pharyngotympanic tube is from several sources. Branches arise from the ascending pharyngeal artery (a branch of the external carotid artery) and from two branches of the maxillary artery (the middle meningeal artery and the artery of the pterygoid canal).
Venous drainage of the pharyngotympanic tube is to the pterygoid plexus of veins in the infratemporal fossa.
Innervation of the mucous membrane lining the pharyngotympanic tube is primarily from the tympanic plexus because it is continuous with the mucous membrane lining the tympanic cavity, the internal surface of the tympanic membrane, and the mastoid antrum and mastoid cells. This plexus receives its major contribution from the tympanic nerve, a branch of the glossopharyngeal nerve [IX].
The bones of the middle ear consist of the malleus, incus, and stapes. They form an osseous chain across the middle ear from the tympanic membrane to the oval window of the internal ear (Fig. 8.123).
Muscles associated with the auditory ossicles modulate movement during the transmission of vibrations.
The malleus is the largest of the auditory ossicles and is attached to the tympanic membrane. Identifiable parts include the head of the malleus, neck of the malleus, anterior and lateral processes, and handle of the malleus (Fig. 8.123). The head of the malleus is the rounded upper part of the malleus in the epitympanic recess. Its posterior surface articulates with the incus.
Inferior to the head of the malleus is the constricted neck of the malleus, and below this are the anterior and lateral processes:
The anterior process is attached to the anterior wall of the middle ear by a ligament.
The lateral process is attached to the anterior and posterior malleolar folds of the tympanic membrane.
The downward extension of the malleus, below the anterior and lateral processes, is the handle of the malleus, which is attached to the tympanic membrane.
The second bone in the series of auditory ossicles is the incus. It consists of the body of the incus and long and short limbs (Fig. 8.123):
The enlarged body of the incus articulates with the head of the malleus and is in the epitympanic recess.
The long limb extends downward from the body, paralleling the handle of the malleus, and ends by bending medially to articulate with the stapes.
The short limb extends posteriorly and is attached by a ligament to the upper posterior wall of the middle ear.
The stapes is the most medial bone in the osseous chain and is attached to the oval window. It consists of the head of the stapes, anterior and posterior limbs, and the base of the stapes (Fig. 8.123):
The head of the stapes is directed laterally and articulates with the long process of the incus.
The two limbs separate from each other and attach to the oval base.
The base of the stapes fits into the oval window on the labyrinthine wall of the middle ear.
Muscles associated with the ossicles