2. THE TYMPANIC CAVITY
 It is like a six sided box –
1. Roof (Tegmental wall)
2. Floor (jugular wall)
3. Lateral wall(Membranous wall)
4. Medial wall (Labyrinthine wall)
5. Posterior wall (Mastoid wall )
6. Anterior wall(Carotid wall)

3. R00F OF TYMPANIC CAVITY
 Formed by tegmen tympani which separates the
middle ear space from the middle cranial fossa
 It is formed by both petrous and squamous part
 Veins to superior petrosl nerve passes through
petrosquamous suture
 This suture line not closed till adult life, so is
a route of infection into extradural space in
children.

4. FLOOR OF TYMPANIC CAVITY
 It is formed by pneumatised bone, or may be
deficient when covered by muscle or mucous
membrane
 It separates from jugular bulb
 At the junction of floor and
medial wall a small opening
present
 Its passes tympanic branch of
glossopharyngeal nerve

5. LATERAl
WALL OF TYMPANIC CAVITY
 It is formed by-
 Superiorly-bony lateral wall of
epitympanum
 Centrally-tympanic mmbrane
 Inferiorly-bony lateral wall of
hypotympanum

6. LATERAL WALL OF TYMPANIC CAVITY
 Lateral epitympanic wall-
 Wedged shaped
 Sharped inferior portion called
scutum, which is very thin &
easily eroded by choleteotoma.
 Petrotympnic fissure-
Open anteriorly just above
attachment of tympanic
membrane. Its-
 receives anterior malleolar
ligament
 Transmit anterior tympanic branch
of maxillay artery

7. LATERAL WALL OF TYMPANIC CAVITY
 Chorda tympani nerve-
 Enters through anterior canaliculus
 Runs posteriorly between the fibrous
and mucosal layers of tympanic
membrane
 Enters posterior canaliculus
 Runs obliquely downwards and
medially through the posterior
wall to reach facial nerve
 Point of entry to facial nerve is
variable, usually inferior 13 rd
of facial canal in ant surface

8. ANTERRIOR WALL OF TYMPANIC CAVITY
 Lower third-
 Consists of thin bone covering
internal carotid artery
 It is perforated by sup.& inf.
corticotympanic nerve carrying
sympathetic fibres to tympanic
plexux from internal carotid
artery

9. ANTERIOR WALL OF TYMPANIC CAVITY
 Middle third-
Comprise tympanic opening of the
Eustachian tube(5mm*2mm)
 Upper third-canal
containing the tensor tympani
muscle
Small niche anterior to ossicular
head called anterior epitympanic
recess-which can hide residual
cholesteotoma

10. MEDIAL WALL OF TYMPANIC CAVITY
 Central portion occupied by a
rounded elevation- called
promontory.
 A small Groove over it contains
tympanic plexus

11. MEDIAL WALL OF TYMPANIC CAVITY
 Behind & above the
promontory, lies oval
window.
 Oval window connects
tympanic cavity with
vestibule.But it is closed by
foot plate of stapes
 It is kidney shaped(3.25 mm
long & 1.75 mm wide)

12. MEDIAL WALL OF TYMPANIC CAVITY
 The round window is
triangular in shape
 It has Ant., Post-Sup, &
Post-Inf wall
 about 2.3*1.9 mm size
 Separated from scala
tympani by secondary
tympanic membrane

13. MEDIAL WALL OF TYMPANIC CAVITY
 Posterior extension of
promontory-Subiculum
 Post-Sup & Post-Inf walls
of round pos window
meets posteriorly & forms-
Sinus Tympani
 It is most inaccessible part of
middle ear & mastoid

14. MEDIAL WALL OF TYMPANIC CAVITY
 Fllopian canal or facial canal
runs above pomontory and oval
window in an antero posterior
direction.
 Anterior most part of the canal is
processus cochleariformis which
attached to tendon of tensor
tympani muscle
 Behind the oval window, the
facianl canal starts to tur
inferiorly as it begins to descent
in the post wall

15.  Smooth lateral surface of facial canal may
have microdehicense, which diagnosed by
visibility of some straight blood vessel over
canal

16.  Above processus cocleaformis
a small swelling corresponds to
genuculate ganglion
 More posteriorly facial nerve
related to lateral semicircular
canal
 During cortical
mastoidectomythe triangular
realationship between lat
semicircular canal,short process
of incuss &facial nerve is very
helpful

17. POSTERIOR WALL OF TYMPANIC CAVITY
 Upper part has a irregular
opening-aditus of antrum
 Below the aditus is the Fossa
incuidis-which houses short
process of incuss and its
suspensory ligament
 Below fossa incuidis ,a conical
projection called Pyramid-attached
to stapedius muscle
& tendon

18. POSTERIOR WALL OF TYMPANIC CAVITY
Facial recess- bounded
medially by the facial
nerve and laterally by the
tympanic annulus
It allows posterior
tympanotomy