The adult temporal bone is made up of five
major components, namely the squamous part
(squama), the petrous part (petrosa), the
tympanic bone, the mastoid process, and the
However, of these five components, the
mastoid and styloid processes do not fully
develop until after birth.
Both the squama and the tympanic bone are
products of membranous bone development.
The petrous portion is represented by the
cartilaginous otic capsule until 20 weeks of
gestation during which ossification proceeds.
The styloid process also is preformed in
It is not until the eight-week stage that one can
first discern development of the squama of the
temporal bone as commencing from an
ossification center which extends into the
The tympanic part of the temporal
bone begins its development at about
9 to 10 weeks of gestation.
In the ninth week, the squama and
zygomatic process begin membrane
By the end of the ninth week, the
superior wall of the middle ear
emerges as a projection of the otic
capsule; known as the superior
periotic process. It grows forward
over the ossicles forming the lateral
aspect of the tegmen tympani.
The medial part of the tegmen
tympani consists of a fibrous tissue
A coronal section of the Skull of a Foetus, 4 months old
DEVELOPMENT AFTER 16 WEEKS
16 weeks-the postauditory process of the squama extends
posterior to the tympanic ring forming the anterosuperior
portion of the mastoid process.
20th to 24th week- a)the petrous bone, composed of the
cartilaginous otic capsule, begins rapid ossification from
b) At this point, the tympanic cavity
and labyrinth have attained full size; however, the temporal
bone, especially the mastoid process, continues to grow.
25 weeks-the floor of the middle ear develops, either as an
independent bone located between the pyramid and the
tympanic ring or as a bony lamellar projection of the
29th week- the tympanic process of the squama joins the
antral segment of the periosteal otic capsule to form the
lateral wall of the antrum.
At term an ossification center forms at the dorsal aspect of
Reichert’s cartilage which fuses with the otic capsule to
create the styloid eminence in the floor of the tympanic
cavity and also part of the distal segment of the bony
The external petrosquamous fissure demarcates the
border between that part of the mastoid derived from the
squama and the portion which arises from the petrosa.
This fissure is visible in the newborn, but generally
disappears by the second year of life.
At birth the mastoid antrum is large with a thin shell of
The mastoid process develops as a prominence on the
outer aspect of the petrous pyramid during the first year
of life. As the mastoid grows, the antrum shrinks in
relative size and assumes a more medial position, as does
the facial nerve. The mastoid, although well developed by
three years of age, does not achieve adult configuration
for several more years.
Postnatally, the styloid process forms as an ossification
center in the upper portion of Reichert’s cartilage;
concurrently, at its ventral aspect another ossification
center appears which will become the lesser horn of the
hyoid and the superior part of the body of the hyoid.
The fusion of the separate components of the temporal
bone then becomes the major process in its further
In children the pinna needs to be pulled backwards, downwards and
laterally to make the external auditory canal in line for examination as the
developing temporal bone is horizontally placed which becomes vertically
placed in adult.
The mastoid process in children is not fully developed, thus cannot be
palpated easily. Hence the postauricular incision in children should be
given more horizontally to prevent injury to the facial nerve.
POST AURICULAR INCISION IN ADULT VS INFANT
The temporal bone is a composite structure
1. The Tympanic Bone
2. The Mastoid Process
3. The Squama(Squamous portion of the
4. The Petrosa(Petrous portion of the
ACCORDING TO SHAMBAUGH
TEXTBOOK OF SURGERY OF THE EAR ,
ALTHOUGH THE STYLOID PROCESS IS
CLOSELY RELATED TO THE TEMPORAL
BONE, IT IS NOT CONSIDERED A
PORTION OF IT.
TEMPORAL BONE (LATERAL SURFACE)
The four parts visible here are:
1) squamous bone - flattened region that forms the lateral
portion of the skull and is the origin for the temporalis muscle.
The zygomatic process extends anteriorly from the squamous
2) tympanic bone - forms the floor, anterior and inferior wall of
the bony portion of the external auditory canal
3) styloid bone - a slender process of variable length that
extends in an anterior-inferior direction and serves as the
attachment for the stylohyoid, styloglossus and stylopharyngeus
4) mastoid bone
Immediately in front of the external auditory meatus is the
glenoid (mandibular) fossa where the condyle of the mandible
Also visible on the lateral side of the temporal bone are
Macewen’s (suprameatal) triangle (i.e., a shallow depression
posterior-superior to the EAM that marks the position of the
mastoid antrum) and the spine of Henle which is a projection of
variable prominence at the posteriosuperior aspect of the
external auditory canal.
LATERAL SURFACE OF RIGHT TEMPORAL BONE
It forms the anterior, inferior and parts of the posterior wall of the external
It interfaces with 1) the squama at the tympanosquamous suture,
2) the mastoid at the tympanomastoid suture and
3) the petrosa at the petrotympanic fissure and constitutes
the posterior wall of the glenoid fossa for the temporomandibular joint (TMJ).
The chorda tympani nerve, anterior process of the malleus, and anterior
tympanic artery traverse the petrotympanic fissure.
Inferiorly, the vaginal process, a projection of tympanic bone, forms the
sheath of the styloid bone.
Laterally, the tympanic bone borders the cartilaginous EAC, whereas
medially it bears a circular groove, the annular sulcus. The annular sulcus
houses the annulus of the tympanic membrane except superiorly, where it is
deficient; at this point, known as the notch of Rivinus, the tympanic
membrane attaches directly to the squama.
Anteriorly, the tympanic ring separates the external auditory canal from the
glenoid fossa, which lies beneath the root of the zygoma.
Temporomandibular joint dysfunction, as well as disease of the molar teeth, may
manifest in referred otalgia, owing both to the proximity of the EAC and the
shared innervation by the mandibular division of the trigeminal (fifth cranial)
SQUAMOUS PORTION OF TEMPORAL BONE
• It serves as the lateral wall of the middle cranial fossa and
interfaces with the parietal bone superiorly and with the
zygomatic process and the sphenoid anteriorly.
• Its medial surface is grooved by a sulcus for the middle
meningeal artery, whereas the middle temporal artery runs in a
groove on its lateral aspect.
MASTOID PORTION OF THE TEMPORAL BONE
• It is the inferiorly extending projection seen on the lateral surface
of the temporal bone. It is composed of a squamous portion
(laterally) and a petrous portion (medially) separated by Körner’s
• The fossa mastoidea (Macewen’s triangle) is defined by the linea
temporalis (temporal line), the posterosuperior margin of the
external auditory canal, and a tangent to the posterior margin of
the external auditory canal.
• The fossa mastoidea, a cribrose (cribriform) area, is identified by
its numerous, perforating small blood vessels.
• The mastoid foramen, located posteriorly on the mastoid process,
is traversed by the mastoid emissary vein and one or two mastoid
• Inferiorly, the sternocleidomastoid muscle attaches to the mastoid
The styloid process is a slender pointed piece of
bone just below the ear. It projects down and
forward from the inferior surface of the temporal
bone, and serves as an anchor point for several
muscles associated with the tongue and larynx.
Its proximal part (tympanohyal) is ensheathed by
the vaginal process of the tympanic portion.
Its distal part (stylohyal) gives attachment to the
styloglossus muscle (innervated by the
stylohyoid muscle (innervated by the facial
stylopharyngeus muscle (innervated by the
The tympanosquamous and tympanomastoid sutures are landmarks for the
“vascular strip” incisions used in tympanomastoid surgery. The elevation of
EAC skin and periosteum at these two sutures often requires sharp dissection to
divide the contained periosteum, particularly at the tympanosquamous suture.
Elevation of the tympanic membrane, as for a transcanal exploratory
tympanotomy, typically commences just above the notch of Rivinus; the surgeon
is thus able to identify the annulus and elevate the tympanomeatal flap in
continuity with the tympanic membrane.
The tip of the mastoid process is easily palpated and is a landmark for the
positioning of postauricular incisions.
The zygomatic process is also readily identifiable. The posterior root of
zygomatic process forms the suprametal crest and the anterior root ends in a
rounded eminence, the articular tubercle (eminentia articularis) which articulates
with the mandible and gives attachment to the masseter muscle. On occasion,
posterior bulging of the anterior canal wall may obscure full visualization of the
tympanic membrane. Anterior canalplasty can improve surgical visualization but
if overzealous may result in prolapse of the TMJ into the EAC with, for
example, opening the mouth.
The tympanomastoid fissure is anterior to the tip of the
mastoid and can be traced medially to the stylomastoid
foramen, which is the exit point of the facial nerve. Thus,
caution must be exercised when dissecting anterior to the
mastoid tip during mastoid surgery, particularly in young
children in whom the tip is not well developed.
Vestibular schwannoma, Middle cranial fossa
approach- It is utilized primarily for the purpose of hearing
preservation in patients with small tumors, typically confined
to the internal auditory canal. A small window of squamous
part of temporal bone is removed to allow exposure of the
tumor from the upper surface of the internal auditory canal,
preserving the inner ear structures.
1. The stylomandibular ligament is a specialized band of the
cervical fascia, which extends from near the apex of the
styloid process of the temporal bone to the angle and
posterior border of the angle of the mandible. This
ligament separates the parotid from the submandibular
gland and medial pterygoid.
2. Eagle syndrome is characterized by recurrent pain in the
oropharynx and face due to an elongated styloid process
or calcified stylohyoid ligament. which interferes with
adjacent anatomical structures giving rise to pain.
• A prominent ridge known as the
temporal line (linea temporalis) runs
posteriorly and slightly superiorly from
the root of the zygoma and defines the
inferior border of the temporalis
• The linea temporalis is an avascular
plane, a feature that makes it an ideal
location for the superior limb of the
“T” musculoperiosteal incision used in
the postauricular approach to the
• The squamous portion of the temporal
bone (the squama) extends above the
temporal line, whereas inferiorly and
anteriorly is the tympanic ring and
posteriorly the mastoid.
• The temporal line also approximates
the position of the floor of the middle
•The posterior meatal skin is firmly adherent to
the tympanmastoid suture, as such sharp and
careful dissection should be carried out in this
region to prevent tear of the tympanomeatal
•The facial nerve lies 8mm medial to the
•The tympanomastoid suture is traversed by
Arnold’s nerve (auricular branch of vagus
FOSSA MASTOIDEA (MACEWEN’S
• Macewen’s triangle (the fossa mastoidea), is
delineated by the temporal line superiorly, a tangent
to the posterior external auditory canal posteriorly,
and the posterosuperior rim of the canal.
• Macewen’s triangle is characterized by the presence
of multiple small perforating vessels and hence is
also known as the cribrose (cribriform) area. The
mastoid antrum, medial to the fossa mastoidea
(Macewen’s triangle), develops in the earliest stages
of mastoid pneumatisation and is ordinarily present
in even the least pneumatised temporal bones.
• The fossa mastoidea is an important surgical
landmark as it laterally overlies the mastoid antrum.
Therefore, the fossa mastoidea is the site at which
mastoid drilling ordinarily commences.
• Henle’s spine which marks the anterior and inferior
limit of dissection in a canal wall up
mastoidectomy, is a content of the macewen’s
TEMPORAL BONE (MEDIAL SURFACE)
It features the porus of the internal
auditory canal (IAC).
The foramen seen at the petrous apex
is the internal carotid foramen, by
which the internal carotid artery exits
the temporal bone.
The sigmoid portion of the lateral
venous sinus runs in the deep sulcus
seen posteriorly, whereas the superior
petrosal sinus runs in the sulcus located
at the junction of the posterior and
middle fossa faces of the temporal
The petrous portion of the temporal
bone houses part of the middle ear
(e.g., ossicles) and inner ear (i.e.,
cochlear and vestibular end organs).
Left adult temporal bone, medial
aspect. 3 = squama; 11 = middle meningeal
arterial sulcus; 12 = petrous bone; 13 = internal
auditory canal; 14 = sigmoid sulcus; 15 = superior
petrosal sulcus; 16 = inferior petrosal sulcus;
17 = petrous apex; 18 = arcuate eminence; 19
= internal carotid artery foramen.
The following landmarks are visible on the
1) cochlear aqueduct - a fine canal that connects
scala tympani in the basal turn to the
cerebrospinal fluid (CSF) space around the brain
2) vestibular aqueduct - a bony passage that runs
from the vestibule to the subarachnoid space. It
transmits the endolymphatic duct
3) internal auditory meatus (IAM) - a bony
opening through which the 7th (i.e., facial) and 8th
(i.e., vestibulocochlear) cranial nerves and
internal auditory artery enter the petrous part of
the temporal bone
4) mastoid process
5) sigmoid sinus sulcus - an ‘s’-shaped
depression on the medial side of the temporal
bone that is located posterior to the operculum
and vestibular aqueduct. The sigmoid sinus is
continuous with the transverse sinus and empties
into the internal jugular vein
6) styloid process.
7) The jugular fossa marks the location of the
The temporal bone contains the air space
of the middle ear and air cells in the
mastoid, petrosa, perilabyrinthine and
TEMPORAL BONE (POSTERIOR SURFACE)
The vertically oriented posterior face of the petrosa dominates the posterior
view of the temporal bone as it delimits the anterolateral aspect of the posterior
cranial fossa and lies between the superior and inferior petrosal sinuses.
The porus of the IAC, operculum, endolymphatic fossette cradling the
endolymphatic sac, and subarcuate fossa are the key anatomic features on this
A view of the posterior surface of a left
< Posterior lip,
AE Arcuate eminence,
AFL Anterior foramen
lacerum component of the petrous apex,
ELD Endolymphatic duct foramen,
IAC Internal auditory canal,
JB Jugular bulb,
SP Styloid process,
SS Sigmoid sinus groove
ACF Anterior condylar foramen,
ELD Endolymphatic duct foramen,
FM Foramen magnum,
FO Foramen ovale,
FR Foramen rotundum,
FS Foramen spinosum,
IAC Internal auditory canal,
JF Jugular foramen,
JT Jugular tubercle,
OB Occipital bone,
OC Occipital condyle,
PB Parietal bone,
PCF Posterior condylar foramen,
PR Petrous ridge,
SB Squamous bone,
SS Sigmoid sinus grooveA view of the posterior surface of an articulated temporal
The posterior surface of the temporal bone
forms the anterior border of the posterior
The sigmoid sulcus is an indentation at the
lateral aspect of the posterior surface and
accommodates the sigmoid sinus.
Anterior to the sigmoid sulcus is the foveate
fossa for the intradural portion of the
endolymphatic sac. A ledge at the superior
extent of the fossa, the operculum, covers the
intraosseous portion of the endolymphatic sac.
The vestibular aqueduct runs anteriorly,
superiorly, and medially from the operculum to
end at the medial wall of the vestibule.
The superior petrosal sulcus, located at the
interface of the posterior and middle cranial
fossa plates of the temporal bone, carries the
superior petrosal sinus from the sigmoid sinus
to the cavernous sinus anteriorly.
The internal auditory canal penetrates the posterior surface of the petrous ridge, runs anteromedially
to posterolaterally, and contains the cochlear, vestibular, and facial nerves, along with their blood
supply. The canal extends approximately 1 cm from the porus medially to the fundus laterally. At the
fundus, the canal is divided into an upper and a lower portion by the transverse crest (crista
falciformis). The inferior compartment contains the cochlear nerve anteriorly and the inferior
vestibular nerve posteriorly. A vertical crest of bone, Bill’s bar, separates the superior portion of the
canal into an anterior compartment, occupied by the facial nerve, and a posterior compartment
containing the superior vestibular nerve.
A branch of the inferior vestibular nerve, the posterior ampullary nerve or singular nerve , which
innervates the ampulla of the posterior semicircular canal, exits the internal auditory canal through the
In rare cases of chronic persistent positional vertigo which do not respond to physiotherapy singular
nerve neurectomy is a new surgical procedure for treatment.
The inferior surface of the temporal bone
separates the upper neck from the skull base.
Accordingly, many vital
neurovascular structures traverse this surface.
Anteriorly and medially, the carotid foramen is
the point at which the internal carotid artery
enters the temporal bone.
Posteriorly, a ridge of bone, the jugulocarotid
crest, separates the carotid canal from the
Classically, the jugular foramen has been
thought of as being divided into a posterolateral
pars venosa, which is occupied by the jugular
vein, and an anteromedial pars nervosa, which
is traversed by the glossopharyngeal, vagus, and
spinal accessory nerves.
The hypoglossal nerve exits the occipital bone
by the hypoglossal canal, medial to the pars
nervosa of the jugular foramen.
Lateral to the jugular foramen is the styloid
Immediately posteriomedial to the styloid
process is the stylomastoid foramen, by which
the facial nerve exits the temporal bone.
TEMPORAL BONE (INFERIOR SURFACE)
The triangular opening of the cochlear aqueduct is
located medial to the jugular foramen.
The inferior tympanic canaliculus runs in the
jugulocarotid crest and carries the inferior
tympanic artery (a branch of the ascending
pharyngeal artery) and the tympanic branch of the
glossopharyngeal nerve (Jacobson’s nerve) into the
An inferior view of an articulated temporal bone.
AFL Anterior foramen lacerum, BO Basiocciput, CF
Carotid foramen, DR Digastric
ridge, FM Foramen magnum, GF Glenoid fossa, GWS
Greater wing of
the sphenoid, MT Mastoid tip, O Foramen ovale, OB
OC Occipital condyle, PCF Posterior condylar foramen,
S Foramen spinosum,
SMF Stylomastoid foramen, ZP Zygomatic process
The cochlear aqueduct runs from the medial
aspect of the scala tympani of the basal
cochlear turn to terminate anteromedial to the
jugular bulb, it parallels, and lies inferior to,
Foramen Lacerum- Structures passing whole
1. Meningeal branch of Ascending pharyngeal
2. Emissary vein
Other structures partially traversing:
3. Internal carotid artery
4. Greater petrosal nerve
1.Mandibular Nerve (CN V3)
2. Accessory meningeal nerve
3. Lesser petrosal nerve
4. Emissary vein (Cavernous sinus to pterygoid
5. Occasionally anterior trunk of middle
1. Middle meningeal artery and vein (posterior
2. Emissay vein
3. Nervus spinosus (Meningeal branch of
The jugular foramen is of particular
importance in skull base surgery as it is
traversed by the glossopharyngeal (ninth),
vagus (tenth), and spinal accessory
(eleventh) cranial nerves as they exit the
skull .In the course of posterolateral skull
base exposure, decortication and fibrous
tissue dissection reveal the internal jugular
vein, its bulb, and the internal carotid artery.
Posterior retraction of the internal jugular
vein and resection of the jugular bulb allow
visualization of the lower cranial nerves
exiting the skull (IX,X,XI).
Glomus jugulare tumors are rare, slow-
growing, hypervascular tumors that arise
within the jugular foramen of the temporal
PHELP'S SIGN - loss of crest of bone as
seen in CT-scan between carotid canal and
jugular canal in glomus jugulare.
A close-up view of the jugular foramen–carotid
on the inferior aspect of a left temporal bone.
* Jugulocarotid spine,
< Cochlear aqueduct canal,
> Jacobson’s nerve canal,
AN Arnold’s nerve canal,
D Dome of the jugular bulb,
ICA Internal carotid artery canal,
IPS Groove for the inferior petrosal sinus,
SP Styloid process
From the transmastoid perspective, the cochlear aqueduct is encountered when drilling medial to the
jugular bulb; opening the aqueduct results in the flow of cerebrospinal fluid into the mastoid, a useful
maneuver in translabyrinthine cerebellopontine angle tumor surgery as it decompresses cerebrospinal
In addition, cranial nerve IX, the inferior petrosal sinus, and, in some cases, cranial nerves X and XI
can be found immediately inferior to the lateral terminus of the cochlear aqueduct. Therefore, the
cochlear aqueduct can be used as a guide to the lower limits of IAC dissection in, for example, the
translabyrinthine approach as it allows full exposure of the IAC without risking the lower cranial
Medial to the mastoid tip is the digastric groove for the posterior belly of the digastric muscle.
1) This is an important landmark for the identification of facial nerve during parotid surgery.
2) This projects as the digastric ridge in the mastoid cavity which anteriorly traced leads to the
stylomastoid foramen which delineates the vertical portion of the facial nerve.
TEMPORAL BONE (ANTERIOR SURFACE)
The petrous apex is the wedge of bone that
separates the greater wing of the sphenoid
from the occipital bone.
The most prominent feature of this surface is
the internal carotid foramen, through which
the carotid artery exits the temporal bone.
The impression for the trigeminal ganglion is
located on the lateral surface of the petrous
The semi canal for the tensor tympani is
lateral to the carotid canal; the bony portion
of the Eustachian tube runs inferior and
parallel to the tensor tympani muscle.
The thin medial wall of the eustachian tube
forms the lateral wall of the carotid canal and
is frequently dehiscent. Thus, the carotid
canal is vulnerable to injury in the course of
surgical manipulations in the anterior
tympanic cavity and in the medial wall of the
TEMPORAL BONE (SUPERIOR SURFACE)
The superior surface (tegmen) of the temporal
bone is the floor of the middle cranial fossa,
separating the tympanomastoid compartment
from the temporal lobe.
The tegmen can be divided into
1) an anterior tegmen tympani (covering
the tympanic cavity) and
2) a posterior tegmen mastoideum
(covering the mastoid air cells).
The petrotympanic suture line forms the
medial boundary of the tegmen.
Further medially, the dense petrous bone
(petrosa) runs an oblique course from lateral
to medial. The petrous portion of the temporal
bone is marked by depressions and eminences
corresponding to the convolutions of the brain
and the internal structures of the temporal
The greater petrosal nerve (GPN) separates
from the geniculate ganglion and emerges
through the facial hiatus to run in a groove
that is slightly medial to the petrotympanic
suture and that parallels the petrous ridge.
Lateral to and paralleling the greater petrosal
nerve is the lesser petrosal nerve, which runs
in the petrosquamous suture (superior
The tensor tympani muscle is inferior to the
lesser petrosal nerve.
The foramen lacerum, located at the junction of
the base of the greater wing of the sphenoid, the
petrous apex, and the basiocciput, is a false
foramen that is filled with fibrous connective
tissue and that forms the roof of the carotid canal.
The carotid canal also parallels the petrous ridge.
The gasserian (semilunar) ganglion lies in a
depression at the lateral aspect of the petrous apex
known as the Meckel’s cave.
Anteriorly, proceeding medially to laterally, are
the foramen ovale (for the mandibular division of
the trigeminal nerve) and the foramen spinosum
(for the middle meningeal vessels and a recurrent
branch of the mandibular nerve); these structures
serve as surgical landmarks for the anterior limit
of the temporal bone.
* Meckel’s cave impression,
AE Arcuate eminence,
AFL Anterior foramen lacerum,
FM Foramen magnum,
FO Foramen ovale,
FR Foramen rotundum,
FS Foramen spinosum, GPN Groove for the greater
PR Petrous ridge, SS Sigmoid sinus sulcus, ZP
A superior view of an articulated temporal bone.
It is evident on superior, medial,
and posterior views of the temporal
The term “petrous” (Greek for
“rocklike”) stems from the extreme
density of its bone, which guards
the sensory organs of the inner ear.
Important landmarks seen on a
superior view are the arcuate
eminence (roughly corresponding
to the superior semicircular canal),
meatal plane (indicative of the
internal auditory canal), foramen
spinosum for the middle meningeal
artery, and facial hiatus (marking
the departure of the greater petrosal
nerve from the anterior aspect of
the geniculate ganglion).
The lesser petrosal nerve, accompanied by
the superior tympanic artery, occupies the
superior tympanic canaliculus, lying lateral to
and paralleling the path of the greater petrosal
nerve to the petrous apex. The petrous apex
points anteromedially and is marked by the
transition of the intrapetrous to the intracranial
internal carotid artery, orifice of the bony
eustachian tube, and, anterolaterally, ganglion
of the trigeminal nerve in Meckel’s cave.
The arcuate eminence, present in about 85% of temporal bones, approximates the
position of the superior semicircular canal (SSCC) and is a key landmark in middle
cranial fossa surgery.
In this region, the dura is firmly adherent on the medial side however laterally it is
loosely adherent. Thus, in case of brain abscess following chronic suppurative otitis
media with complications the pus elevates the dura and tracts anteriorly thereby
causing a swelling in the preauricular region known as POTT’S PUFFY TUMOUR.
In middle cranial fossa approach the arcuate eminence serves as an important
landmark for identification of the internal auditory meatus. The bone anteromedial
to the arcuate eminence and greater superficial petrosal nerve is termed the ‘meatal
plane’ and lies above the inernal auditory canal. It is often marked by a shallow
Superior canal dehiscence syndrome (SCDS) is a rare medical condition of the
inner ear, leading to hearing and balance symptoms in those affected. The
symptoms are caused by a thinning or complete absence of the arcuate eminence.
For relief of pain in trigeminal neuralgia glycerol injection is given in the gasserian
ganglion in this region.
Several large dural venous sinuses are
intimately associated with the temporal bone
and comprise the principal venous drainage
of the brain and cranial vault.
1) The superior sagittal sinus and straight
sinus merge at the internal occipital
2) The right and left transverse sinuses
extend beyond this junction. The right
transverse sinus is primarily the
continuation of the superior sagittal sinus
and thus is generally larger in diameter
than the left transverse sinus, which is
primarily the continuation of the straight
3) The transverse sinuses lie just inferior to
the tentorium and parallel its course.
4) Anteriorly, the superior petrosal sinus
joins the transverse sinus, and this
junction marks the beginning of the
1) The sigmoid sinus is the posterior boundary of the
mastoid cavity. However, in particularly well-
pneumatized bones, accessory air cells may extend
posteriorly beyond the sigmoid sinus. The sigmoid
sinus is most superficial (lateral) at its superior
origin. The middle fossa dura approximates the
superior portion of the sigmoid sinus at the
sinodural angle of Citelli. From the sinodural
angle, the sigmoid sinus runs inferiorly and
medially, with a variable relationship to the bony
labyrinth. At its inferior extent, the sigmoid sinus
rises to the jugular bulb. The jugular bulb exhibits
considerable variability in its height, location, and
relationship to the labyrinth, internal auditory
canal (IAC), and tympanic cavity.
2) The inferior petrosal sinus arises from the medial
aspect of the jugular bulb and runs anteromedially
to the cavernous sinus.
3) The jugular vein exits the skull through the jugular
foramen, accompanied by the vagus,
glossopharyngeal, and spinal accessory nerves.
The internal carotid artery also travels
through the temporal bone. Its
entrance, the carotid foramen, is
medial to the styloid process and
anterior to the jugular foramen. The
internal carotid artery travels
superiorly until it encounters the dense
bone of the cochlea, at which point it
makes a 90-degree bend to run
anteriorly and medially.
The carotid canal forms the medial
wall of the eustachian tube; the
internal carotid artery may be
dehiscent and vulnerable to injury
Rarely, the internal carotid artery may
encroach on the tympanic cavity
Drawing indicating approximate anatomic relationships of the internal
carotid artery, superior petrosal sinus, facial nerve, bony labyrinth, and
ossicular chain (right temporal bone).
Artist’s depiction of the posterior aspect of the
right temporal bone, with neurovascular
Emissary veins are drainage routes of the
dural venous sinuses through the skull that
communicate with the superficial veins of
the scalp. A fairly constant emissary vein,
the mastoid emissary vein, can be found at
the junction of the temporal and occipital
bones and usually communicates with the
occipital or postauricular vein.
Tenderness and edema over the mastoid
are pathognomonic for suppurative
thrombophlebitis of the sigmoid sinus and
reflect thrombosis of the mastoid emissary
The majority of the cranial nerves are in close
anatomic relationship to the temporal bone.
Fifth Cranial (Trigeminal) Nerve
The trigeminal (gasserian, semilunar)
ganglion lies on the lateral aspect of the
anterior petrous apex and indents its surface.
This nerve supplies sensory and motor
innervation to the face.
The first two divisions of the trigeminal
nerve, the ophthalmic and the maxillary, are
The motor branch (portia minor) lies medial
to the sensory branch and joins the third
division, the mandibular, to supply the
muscles of mastication; a small branch
supplies the tensor tympani muscle within the
CRANIAL NERVES IN RELATION TO TEMPORAL BONE
Sixth Cranial (Abducens) Nerve
• The abducens nerve innervates the ipsilateral lateral
• It exits the brainstem from a groove between the
superior medulla and inferior pons and then travels
through Dorello’s canal, which is formed by the
petroclinoid (Gruber’s) ligament and petrous apex.
Inflammatory or neoplastic lesions in the petrous
apex can present with lateral rectus palsy.
Also called Gradenigo-Lannois syndrome and
petrous apicitis, is a complication of otitis media and
mastoiditis involving the apex of the petrous temporal
It consists of a triad of symptoms consisting of
1)periorbital unilateral pain related to trigeminal nerve
2)diplopia due to sixth nerve palsy and
3)persistent otorrhea, associated with bacterial otitis
media with apex involvement of the petrous part of the
temporal bone (petrositis).
Seventh Cranial (Facial) Nerve
Preganglionic parasympathetic fibers
destined for the pterygopalatine and
submandibular ganglions and special
sensory (taste) fibers comprise the nervus
intermedius. This nerve joins the larger,
motor root to form the facial nerve.
In the cerebellopontine angle, the nervus
intermedius lies between the facial and
The facial nerve enters the temporal bone
through the internal auditory canal, which it
exits at the meatal foramen to travel
anteriorly to the geniculate ganglion. This
segment of the facial nerve, the labyrinthine
segment, is the narrowest portion (0.61 to
0.68 mm) of the facial canal.
At the geniculate ganglion, the greater
petrosal sinus travels anteriorly, carrying
parasympathetic fibers to the
The main trunk of the facial nerve turns
posteriorly, inferiorly, and laterally to continue
in its tympanic (horizontal) segment.
The nerve continues in this course until it turns
inferiorly at the lateral semicircular canal
(LSCC; the second genu), marking the terminus
of the tympanic segment and the beginning of
the mastoid segment.
The facial nerve continues to travel inferiorly,
posteriorly, and laterally until it exits the
temporal bone at the stylomastoid foramen.
Although the chorda tympani nerve usually
separates from the mastoid segment of the facial
nerve a few millimeters superior to the
stylomastoid foramen, the exact location of this
separation is quite variable. The chorda tympani
nerve traverses the tympanic cavity to carry
parasympathetic fibers to the submandibular
ganglion and taste fibers to the anterior tongue.
The motor component of the facial nerve
supplies the stapedius, posterior digastric, and
stylohyoid muscles, as well as the muscles of
COURSE OF FACIAL NERVE THROUGH TEMPORAL BONE
SSC: SUPERIOR SEMICIRCULAR
LSC: LATERAL SEMICIRCULAR
EAC: EXTERNAL AUDITORY
VII N. : FACIAL NERVE
Eighth Cranial (Cochleovestibular) Nerve
The axons of the cochlear division of the eighth nerve arise from the bipolar cells of the
spiral ganglion in the cochlea.
From this ganglion, the fibers pass through the modiolus and the foramina of the tractus
spiralis foraminosus and into the anterior-inferior portion of the fundus of the internal
auditory canal, at which point they fuse to form the cochlear nerve.
The vestibular portion of the eighth nerve divides into a superior and an inferior
division in the internal auditory canal. The cell bodies for these nerves are in Scarpa’s
ganglion, also located in the canal.
The superior vestibular nerve innervates the utricle, the superior semicircular canal and
lateral semicircular canal, and the superior saccule. The inferior vestibular nerve
innervates the posterior semicircular canal and the inferior saccule.
Ninth Cranial (Glossopharyngeal) Nerve
The glossopharyngeal nerve exits the upper
lateral medulla and passes through the
jugular foramen, accompanied by the vagus
and spinal accessory nerves.
It carries preganglionic parasympathetic
fibers to the otic ganglion and taste fibers
from the posterior third of the tongue,
general sensory afferents from the
pharyngeal mucosa, and motor fibers to the
The tympanic branch (Jacobson’s nerve) re-
enters the temporal bone through the inferior
tympanic canaliculus and emerges onto the
promontory to merge with sympathetic fibers
at the tympanic plexus, forming the lesser
At the cochleariform process, the lesser
petrosal nerve travels medial to the
semicanal of the tensor tympani muscle to
emerge on the floor of the middle cranial
Tenth Cranial (Vagus) Nerve
The vagus nerve is the longest of the
It arises as 8 to 10 rootlets from the
medulla oblongata; these roots unite into
the vagus nerve, which passes beneath
the flocculus to the jugular foramen and
exits the skull within a dural sheath
shared with the spinal accessory nerve.
Eleventh Cranial (Spinal Accessory)
Cranial and spinal rootlets combine to
form the eleventh nerve.
The spinal component extends to the
level of C5 or C6.
These rootlets ascend through the
foramen magnum into the cranial cavity,
cross the occipital bone, and exit through
the jugular foramen.
The spinal accessory nerve innervates
the sternocleidomastoid and trapezius
Twelfth Cranial (Hypoglossal) Nerve
The twelfth nerve arises from the medulla
and exits the brainstem as a series of rootlets
located between the pyramid and olive.
These rootlets fuse to form the hypoglossal
nerve that exits the posterior cranial fossa
through the hypoglossal canal of the occipital
In many animals some of these parts stay separate through life:
•Squamosal: the squama including the zygomatic process
•Tympanic bone: the tympanic part: this is derived from the angular boneof the reptilian lower jaw
•Periotic bone: the petrous and mastoid parts
•Two parts of the hyoid arch: the styloid process. In the dog these small bones are called tympanohyal
(upper) and stylohyal (lower).
In evolutionary terms, the temporal bone is derived from the fusion of many bones that are often
separate in non-human mammals:
•The squamosal bone, which is homologous with the squama, and forms the side of the cranium in
many bony fish and tetrapods. Primitively, it is a flattened plate-like bone, but in many animals it is
narrower in form, for example, where it forms the boundary between the two temporal fenestrae of
•The petrous and mastoid parts of the temporal bone, which derive from the periotic bone, formed from
the fusion of a number of bones surrounding the ear of reptiles. The delicate structure of the middle ear,
unique to mammals, is generally not protected in marsupials, but in placentals, it is usually enclosed
within a bony sheath called the auditory bulla. In many mammals this is a separate tympanic bone
derived from the angular bone of the reptilian lower jaw, and, in some cases, it has an additional
entotympanic bone. The auditory bulla is homologous with the tympanic part of the temporal bone.
•Two parts of the hyoid arch: the styloid process. In the dog the styloid process is represented by a
series of 4 articulating bones, from top down tympanohyal, stylohyal, epihyal, ceratohyal; the first two
represent the styloid process, and the ceratohyal represents the anterior horns of the hyoid bone and
articulates with the basihyal which represents the body of the hyoid bone.