On its lateral surface, it abuts the
external auditory meatus (ear canal) from which it is separated by the
tympanic membrane (eardrum).
Walls The tympanic cavity is bounded by: • Facing the
inner ear, the
medial wall (or
labyrinthic wall,
labyrinthine wall) is vertical, and has the
oval window and
round window, the
promontory, and the
prominence of the facial canal. • Facing the
outer ear, the
lateral wall (or
membranous wall), is formed mainly by the
tympanic membrane, partly by the ring of bone into which this membrane is inserted. This ring of bone is incomplete at its upper part, forming a notch (notch of Rivinus), close to which are three small apertures: the "iter chordæ posterius", the
petrotympanic fissure, and the "iter chordæ anterius". The iter chordæ posterius (apertura tympanica canaliculi chordæ) is situated in the angle of junction between the
mastoid and
membranous wall of tympanic cavity immediately behind the
tympanic membrane and on a level with the upper end of the
manubrium of the
malleus; it leads into a minute canal, which descends in front of the canal for the
facial nerve, and ends in that canal near the
stylo-mastoid foramen. Through it the
chorda tympani nerve enters the tympanic cavity. The
petrotympanic fissure opens just above and in front of the ring of bone into which the tympanic membrane is inserted; in this situation it is a mere slit about 2 mm. in length. It lodges the anterior process and
anterior ligament of the malleus, and gives passage to the anterior
tympanic branch of the
internal maxillary artery. The iter chordæ anterius (canal of Huguier) is placed at the medial end of the petrotympanic fissure; through it the chorda tympani nerve leaves the tympanic cavity. • The
roof of the cavity (also called the
tegmental wall,
tegmental roof or
tegmentum tympani) is formed by a thin plate of bone, the tegmen tympani, which separates the
cranial and tympanic cavities. It is situated on the
anterior (frontal) surface of the
petrous portion of the
temporal bone close to its angle of junction with the
squama temporalis; it is prolonged backward so as to roof in the
tympanic antrum, and forward to cover in the
semicanal for the
tensor tympani muscle. Its lateral edge corresponds with the remains of the
petrosquamous suture. The
Atticus is the part of the tegmentum tympani where the
stapes and
incus are attached. • The
floor of the cavity (also called the
jugular wall) is narrow, and consists of a thin plate of bone (fundus tympani) which separates the tympanic cavity from the jugular fossa. It presents, near the labyrinthic wall, a small aperture for the passage of the tympanic branch of the glossopharyngeal nerve. • The
posterior wall (or
mastoid wall) is wider above than below, and presents for examination the
entrance to the tympanic antrum, the
pyramidal eminence, and the
fossa incudis. • The
anterior wall (or
carotid wall) is wider above than below; it corresponds with the
carotid canal, from which it is separated by a thin plate of bone perforated by the
tympanic branch of the
internal carotid artery, and by the
deep petrosal nerve which connects the sympathetic plexus on the internal carotid artery with the tympanic plexus on the promontory. At the upper part of the anterior wall are the orifice of the semicanal for the
Tensor tympani muscle and the
tympanic orifice of the auditory tube, separated from each other by a thin horizontal plate of bone, the
septum canalis musculotubarius. These canals run from the tympanic cavity forward and downward to the retiring angle between the
squama and the
petrous portion of the temporal bone.
Development It is formed from the
tubotympanic recess, an expansion of the first
pharyngeal pouch. ==Clinical significance==