Anatomy of temporal bone , Its Embryology & Development

1. ANATOMY OF TEMPORAL BONE
BY Dr. VIJAY KUMAR

2.  The paired
temporal bones
contribute to both
the base and the
lateral wall of the
skull.
 For cranial cavity
each forms part of
the middle and
posterior cranial
fossae.

3.  Each bone is divisible
into the following four
parts:
1.Squamous
2.Mastoid
3.Petrous
4.Tympanic
When the pores of the
external acoustic
meatus is taken as a
point of topographical
referrence,the
squamous part is
directed upward
the mastoid part
backward
the tympanic forward
and downward
the petrous portion
medially.

4. The temporal bone articulates with :
 Sphenoid bone
 Parietal bone
 Occipital bone
 Zygomatic bone.

6. The Squamous Part
The squama is
a vertical
plate,the
semicircular
free border of
which is serrate
on
anterosuperior
portion and
bevelled from
within.

7.  The Lateral Surface:
It is smooth and gives
attachment to
temporalis muscle.
zygomatic process
projects from the lower
part of the surface for
attachment of
masseter muscle.
Mandibular fossa is
situated below the root
of the zygomatic
process.
The sulcus for middle
temporal artery passes
upward on the
posterior part of the
squama.

10.  The medial
surface: is
directed towards
the middle
cranial fossa
presents with
impressions for
the cerebral sulci
and gyri and a
deep sulcus for
the middle
meningeal

11. The Mastoid Part
 This is a thick
conical projection
from the
squamous and
petrous parts of
the temporal bone
and it comes into
appostion with
occipital and
parietal bones

12.  The lateral
surface: is
rough and
gives
attachment
to posterior
auricular
and
occipital
muscles.

13.  It has one or more foramina(Mastoid foramen) for
transmission of the mastoid branch of occipital
artery and the mastoid emissary veins to sigmoid
sinus.
 A small spur ,the suprameatal spine of Henle ,
projects laterally from the posterosuperior margin
of the external acoustic meatus.
 The slightly depressed surface behind the spine
is mastoid fossa,it is perforated by numerous
blood vessels.
 A thick downward directed portion,the mastoid
process,gives attachment to the musculature of
shoulder girdle and of the back.

16.  The medial
surface:
presents a
deep groove
,the sigmoid
sulcus for
lodgement of
the sigmoid
venous sinus
of the dura
mater.

17.  Within the
process are
numerous
cavities,the
mastoid air
cells lined by
mucous
membrane that
is continuous
with that of
tymanic cavity.

18. The petrous part
 This part of the temporal bone is like a
three sided pyramid.
 The base united with the mastoid part
is inserted into the angle between
occipital and sphenoid bones.
 The apex is directed medially and
forward.

20. The foramen lacerum intervenes between the
apex and the sphenoid bone .
Structure passing whole length:
 Meningeal branch of ascending pharyngeal
artery
Emissary veins
Other structure partialy traversing is :
 Internal carotid artery with venous and
sympathetic plexus around it.
Greater petrosal nerve unite with dep petrosal
nerve to form nerve to pterygoid canal

21. The petrous part…

22. The Petrous part has got three surfaces:
Anterior
Posterior
Inferior.

23.  The anterior surface:
It is smooth , forms part of the middle
cranial fossa and inclines forward and
downward.
 Laterally it is fused with squama at the
petrosquamous suture.
The petrous part…

25. The petrous part…
 The anterior margin(termed the anterior
angle) is free & roughened , with the
greater wing of the sphenoid bone bounds
an opening : the musculotubal canal
 Canal is subdivided by leaflet of bone into
smaller upper part - the semicanal for the
tensor tympani muscle
and
a large lower portion the semicanal of
auditory(eustachian ) tube

27.  Near the middle of the anterior surface is
the Arcuate eminence ,caused by
underlying superior semicircular canal.
 Anterior and lateral to this eminence is the
tympanic tegmen,which forms the roof of
the tympanic cavity.

30.  In the anterior direction near the apex is
a medial opening, hiatus of the facial
canal
(it transmits the superficial petrosal
branch of the middle meningeal artery
and the greater superficial petrosal
nerve)
and
a lateral smaller opening, superior
aperture of the tympanic canaliculus(it
transmits the superior tympanic artery
and the lesser superficial petrosal nerve)

33. The posterior surface:
 It lies in an almost vertical plane and it
faces the posterior cranial fossa.
 It is bounded above at the superior angle
by the sulcus for superior petrosal sinus,
 below at the posterior angle ,the pyramid
unites with the occipital bone ,along the
line of fusion accommodating the sulcus
for inferior petrosal sinus.

35.  Midway between the base and apex is the
opening of internal acoustic meatus(short
canal for acoustic and facial nerves and the
internal auditory blood vessels)
 Behind and above this is the subarcuate
fossa (it carries blood vessels to otic
capsule during fetal life.) it is of pin point
caliber in adults and may transmit small
veins to dura mater.
 Further laterally and downward is the
vestibular aqueduct (for transmission of
endolymphatic duct and sac)

37. The inferior surface :
 The inferior surface of pyramid lies in horizontal
plane.
 With occipital bone this surface forms the jugular
foramen

38.  The lateral
part of the
foramen
contains the
junction of
sigmoid sinus
and the
internal
jugular vein
 Medial part
contains
inferior
petrosal sinus
and middle
portion
contains
cranial
nerves IX,X
and XI.

39.  In front of the lateral compartment of the
foramen is jugular fossa (for the bulb of
jugular vein).
 Medial to fossa is the funnel-shaped
external aperture of the cochlear canaliculus
(containing perilymphatic duct).
 In front of the fossa is the external carotid
foramen(entrance to the canal for the
internal carotid artery and its plexus of veins
and sympathetic nerves.)

41.  Near the external carotid foramen small
openings ,the caroticotympanic canaliculi
are present which transmit the
caroticotympanic artery and nerves into the
middle ear.
 The external carotid foramen is separated
from the jugular fossa by the carotid ridge.
On the edge of the carotid ridge is petrosal
fossula for lodgement of petrosal ganglion
of the glossopharyngeal nerve.
At the bottom of this fossula ,tympanic
canaliculus is situated ,which transmits
tympanic branch of glossopharyngeal nerve
(Jacbson’s nerve) and tympanic branch of
ascending pharyngeal artery.

43.  Rough jugular surface behind the jugular
fossa articulates with the jugular process of
the occipital bone.
 Lateral to this surface,a downward directed
cylindrical spur ,the styloid process is
present.
 The stylomastoid foramen is present at its
base on the posterior aspect.
 This is the external orifice of the facial canal
and transmits the facial nerve ,the
stylomastoid artery and in some cases the
auricular branch of the vagus nerve.

45.  Mastoid
incisure/notch (for
the attachment of
the digastric
muscle) and the
temoral/occipital
groove(for the
occipital artery) is
present in the
posterior direction.

46. The Tympanic Part
 The tympanic bone is thin and roughly
quadrilateral bone.
 It is hollow above and concave in front
and below.
 It forms all the anterior and inferior wall
and part of posterior wall of the external
acoustic meatus.
 The posterosuperior surface faces the
external acoustic meatus and the
tympanic cavity.

48.  The middle of anteroinferior surface is thin &
sometimes presenting a small Foramen of
Huschke.
 It represents a nonossified portion of the
plate.
 At the medial end a groove called tympanic
sulcus is present whichh is deficient
superiorly ,the tympanic membrane is present
in this sulcus.
 The inferior surface is prolonged into a
vaginal process,which encircles the lateral
aspect of the base of the styloid process.

51. Sutures and Articulations
Articulations:
The temporal bone articulates with:
 occipital
 parietal
 Sphenoid
 zygomatic bones and – by a movable
joint- with the mandible.
 Articulations are formed also with the
auditory ossicles and the hyoid bone
through the ligaments.

53. Embryology and Ossification
 The skull is developed from the
mesenchyme surrounding the
developing brain.
 Some of the bones of skull are formed in
membrane, some in cartilage and some
partly in membrane and partly in
cartilage.
 The squamous and tympanic parts of the
temporal bone develop in membrane
while the petrous part in the cartilage.
 The squamous portion of the subsequent
temporal bone is formed from one(or
two) ossification centers which arise in
membrane in the second month of

54.  The tympanic portion has three ossification
centers which appear by ninth to tenth fetal
week.
 The tympanic and squamous part unite by ninth
month of fetal life.
 The petrous bone by the fifth month is
represented by the otic capsule. This bone later
ossifies in 14 centers. (petrous part is formed in
cartilage.)
 squamous and petrous part fuse immediately
after birth.
 The styloid process (formed in cartilage) ossifies
from six months onwards.
 Zygomatic bone arises as a thin bony plate by
ossification in membrane at the end of second
month of embryonic life.

55. Applied anatomy and important
relations
 Glossopharyngeal nerve lies in close relation to
styloid process and Elongated styloid process or
calcified stylohoid ligament may lead to Eagle’s
syndrome or styalgia.(characterised by pain in
tonsillar fossa and upper neck , radiating to
ipsilateral ear and aggravated on swallowing)
 Mac Ewen’s triangle is a landmark for mastoid
antrum and is formed by posterosuperior wall of
external acoustic meatus ,the posterior extension
of the root of zygomatic arch and a tangent to it
joining external auditory canal.
 The position of sigmoid sinus in the sigmoid
sulcus just behind and deep to the mastoid
antrum makes it vulnerable to damage in mastoid
surgeries.

56.  The anterior relation of temporomandibular joint to
external acoustic meatus is important as over
enthusiastic attempts at straightening the anterior canal
wall can lead to sagging of head of mandible in external
auditory canal.
 And for the same reason a backward directed force on
the mandible can cause trauma and bleeding in
external auditory canal(either unilateral or bilateral)
 The intratemporal course of the facial nerve from the
entrance of facial canal at the fundus of internal
acoustic meatus to the stylomastoid foramen is
extremely important in ear surgeries.
 The horizontal semicircular canal ,the processus
cochleariformis , the oval window , the pyramid , the
aditus , digastric ridge and the short process of incus
are few important landmarks which help to identify the
position and course of facial nerve in the temporal
bone.

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