Walls of the Middle Ear

The middle ear (tympanic cavity) is a box-like space with 6 walls. A helpful mnemonic is "TAMIL R" (Tegmental, Anterior, Mastoid, Internal/labyrinthine, Lateral/membranous, Roof-floor pair) -- or just remember them by direction.

1. Tegmental Wall (Roof)

Also called: Roof
Bone: Tegmen tympani - a thin plate of bone on the anterior surface of the petrous part of the temporal bone
Separates the middle ear from the middle cranial fossa
Clinical note: Infection can spread superiorly through this thin plate to cause extradural abscess or meningitis

2. Jugular Wall (Floor)

Also called: Floor
Separates the tympanic cavity from the internal jugular vein (bulb of the jugular vein)
May be thickened by mastoid air cells
Contains a small aperture near the medial border through which the tympanic branch of CN IX (Jacobson's nerve) enters the middle ear
Clinical note: A high-riding jugular bulb can protrude into the floor and appear as a bluish mass behind the tympanic membrane

3. Membranous Wall (Lateral Wall)

Also called: Lateral wall
Formed almost entirely by the tympanic membrane
The tympanic membrane does not extend superiorly into the epitympanic recess, so the upper part of this wall is formed by the bony lateral wall of the epitympanic recess

4. Mastoid Wall (Posterior Wall)

Also called: Posterior wall
Only partially complete
Lower part: bony partition between tympanic cavity and mastoid air cells
Upper part: the epitympanic recess is continuous with the aditus to the mastoid antrum

Key structures associated with this wall:

Structure	Significance
Pyramidal eminence	Small bony projection through which the tendon of stapedius muscle enters the middle ear
Chorda tympani nerve	Branch of CN VII; enters the middle ear through an opening in this wall, crosses the handle of the malleus, exits via the anterior wall

5. Anterior Wall (Carotid/Tubal Wall)

Also called: Carotid wall or Tubal wall
Only partially complete
Lower part: thin layer of bone separating the tympanic cavity from the internal carotid artery
Superior part is deficient, containing two large openings:
1. Large opening for the pharyngotympanic tube (Eustachian tube) entering the middle ear
2. Smaller opening for the canal containing the tensor tympani muscle
Also contains the foramen for exit of the chorda tympani nerve from the middle ear

6. Labyrinthine Wall (Medial Wall)

Also called: Medial wall or Promontory wall
Simultaneously forms the lateral wall of the internal ear
The most complex and clinically important wall

Key features:

Feature	Details
Promontory	Rounded bulge produced by the basal coil of the cochlea; covered by the tympanic plexus (CN IX + sympathetic branches from internal carotid plexus)
Oval window (fenestra vestibuli)	Posterosuperior to the promontory; closed by the footplate of the stapes; transmits vibrations to the perilymph of the vestibule
Round window (fenestra cochleae)	Posteroinferior to the promontory; closed by the secondary tympanic membrane; acts as a pressure release valve for cochlear fluid
Prominence of the facial canal	Ridge of bone posterior and superior to the oval window, produced by CN VII in its bony canal - clinically important as it can dehisce
Prominence of the lateral semicircular canal	Broader ridge just above and posterior to the facial canal prominence

The tympanic plexus on the promontory gives off the lesser petrosal nerve, which travels across the petrous temporal bone, exits via the foramen ovale, and enters the otic ganglion (supplying the parotid gland).

Summary Table

Wall	Other Name	Key Relations / Contents
Roof	Tegmental	Tegmen tympani / Middle cranial fossa
Floor	Jugular	Internal jugular vein; tympanic branch of CN IX
Lateral	Membranous	Tympanic membrane; bony wall of epitympanic recess
Posterior	Mastoid	Aditus to mastoid antrum; pyramidal eminence (stapedius); chorda tympani entry
Anterior	Carotid/Tubal	Internal carotid artery; pharyngotympanic tube; tensor tympani canal; chorda tympani exit
Medial	Labyrinthine	Promontory (cochlea); oval window (stapes footplate); round window; facial canal; lateral SCC prominence

Source: Gray's Anatomy for Students, pp. 1099-1100

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