Faculty of dentistry
T H E F U T U R E S T A R T S H E R E
S p r i n g 2 0 2 2

Dr. Waleed Nasr
Norma basalis
. Dr. Rehab Tolba

Foramen
magnum
Anterior
part
Middle
part
Posterior
part
Norma Basalis Externa

Anterior part
• Formed by the Bony Palate
• The anterior ¾ of the palate is formed by the palatine processes of both maxillae
(separated by the intermaxillary suture)
• The posterior ¼ is formed by the horizontal plates of both palatine bones (separated
by the interpalatine suture)
Palatine processes
of maxillary bones
Horizontal plates
of palatine bones
Interpalatine suture
Intermaxillary suture
Incisive fossa

Features of the anterior part
• Alveolar arch, formed by the alveolar processes of both maxillae
• Palato-maxillary suture, separates the parts forming the hard palate.
• Incisive fossa, an anterior median depression.
• Greater palatine foramen (one on each side), on the posterior and lateral part of the
bony palate. It leads to the greater palatine canal
• Lesser palatine foramina (two small foramina) behind the greater palatine foramen.
• Posterior nasal spine, a median projection from the posterior border of the bony palate
• Maxillary tuberosity :a rough prominence behind the last molar tooth
Incisive fossa
Alveolar arch
Greater palatine
foramen
Lesser palatine
foramina
Posterior nasal
spine
Interpalatine
suture
Palato-maxillary
suture
Intermaxillary suture
Cruciform
suture
Palatine crest

• Body of sphenoid bone
• Basilar part of occipital bone
• Pterygoid process of sphenois
• Greater wing of sphenoid
• Petrous part of temporal bone
• Tympanic part of temporal bone
• Mastoid part of temporal bone
• Mandibular fossa
Body of
sphenoid bone
Petrous part
of temporal bone
Groove for cartilagenous
part of auditory tube
Tympanic part
of temporal bone
Styloid process
Mandibular
fossa
Mastoid part
of temporal bone
Middle part
Extends from the posterior margin of hard palate
to the anterior margin of foramen magnum

Features:
•Vomer, a median bone forming the posterior part of the nasal septum
•Posterior nasal apertures
•Pterygoid process, formed of lateral & medial plates with the pterygoid fossa in between.
•Pterygoid Hamulus
•Pterygomaxillary fissure
•, Infratemporal surface of greater wing of sphenoid
•Pharyngeal tubercle, a small elevation on the basilar part occipital bone
Pterygoid hamulus
Posterior nasal
apertures
Vomer
Medial pterygoid
plate
Lateral pterygoid
plate

Foramina to be identified:
• Foramen ovale, on the infratemporal surface of greater wing of sphenoid
• Foramen spinosum, behind the foramen ovale
• Foramen lacerum, at the apex of petrous temporal bone
• Carotid canal
• Stylomastoid foramen, between the styloid and mastoid processes.
Foramen ovale
Foramen spinosum
Foramen lacerum
Carotid canal
Stylomastoid foramen
Groove for cartilagenous
part of auditory tube

Posterior part
Formed mainly by the different parts of the occipital bone, surrounding the foramen magnum
Bones to be identified:
• Condylar parts, one on each side of foramen magnum
• Squamous part, behind the foramen magnum
Features:
•Occipital condyles, on each side of
foramen magnum
•Condylar fossa, behind the occipital
condyles
•External occipital protuberance
•External occipital crest
•Inferior nuchal lines
•Superior nuchal lines
Basilar
part
Squamous part
Foramen
magnum
Pharyngeal tubercle
Occipital condyles
(condylar part)
External occipital
protuberance
Condylar fossa
Condylar canal
External occipital crest
Inferior nuchal lines
Superior nuchal lines

Foramina:
• Foramen magnum, the largest in the skull
• Jugular foramen, between the occipital and petrous temporal bones
• Hypoglossal canal, above the occipital condyle
• Condylar canal
Foramen
magnum
Jugular foramen
Jugular fossa
Condylar canal
Mastoid foramen

Norma Basalis Interna
Divided into; anterior, middle and posterior cranial fossae
Features of the anterior cranial fossa
• Frontal crest, a median ridge on the inner aspect
of frontal bone
• Cribriform plate of ethmoid bone, in the median
region of the fossa, forming the roof of the nasal
cavity. It shows a median projection called the
crista galli
• Orbital plate of frontal bone, on each side of the
cribriform plate of ethmoid.
• Body of sphenoid bone, behind the cribriform
plate
• Lesser wing of sphenoid, on each side of the
sphenoid bone.
• Anterior clinoid process The medial end of the
lesser wing
Frontal crest
Cribriform plate
of ethmoid
Orbital plate
of frontal bone
Body of sphenoid bone
Lesser wing
of sphenoid Crista galli
Anterior clinoid
process
Anterior cranial fossa
Bound posteriorly by the
lesser wings of sphenoid

Foramina:
• Foramen cecum, between the
crista galli and frontal crest
• Antherior ethmoidal canal, on
the lateral margin of the cribriform
plate of ethmoid
• Posterior ethmoidal canal, at
the posterolateral angle of the
cribriform plate of ethmoid.
Foramen cecum
Antherior ethmoidal
canal
Posterior ethmoidal
canal

Middle cranial fossa
• Bound anteriorly by the lesser wings of sphenoid and posteriorly
by the upper border of petrous temporal bone
• Narrow in the middle and expands greatly laterally
Bones to be identified;
• Body of sphenoid, in the median region
• Greater wing of sphenoid
• Squamous part of temporal bone
• Anterior surface of petrous
temporal bone
Body of
sphenoid
Greater wing
of sphenoid
Squamous part
of temporal bone
Petrous part
of temporal bone
F.
magnum

Features of the middle cranial fossa
Tegmen
tympani
Acruate
eminence
Trigeminal
impression
Groove for ICA Hypophyseal
fossa
Posterior
clinoid process
Foramen
lacerum
Sulcus for
optic chiasma
Anterior clinoid
process
• Hypophyseal fossa (sella turcica), a median depression on the body of sphenoid. Bound
anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae. The upper end of
the dorsum sellae forms two projections (the posterior clinoid processes)
• Groove for Internal Carotid Artery,
on the lateral aspect of the body of sphenoid
• Trigeminal impression,
a depression at the apex of petrous temporal bone
• Acruate eminence, an elevation on the
anterior surface of petrous temporal bone
• Tegmen tympani (roof of the middle ear)
lies lateral to the arcuate eminence.

Foramina and openings in the
middle cranial fossa;
• Superior orbital fissure, a fissure
between the greater and lesser wings of
sphenoid
• Foramen rotundum, behind the
medial end of superior orbital fissure,
leads to the pterygopalatine fossa
• Foramen ovale, behind the foramen
rotundum.
• Foramen spinosum, behind the
foramen ovale
• Foramen lacerum, at the apex of
petrous temporal bone
Superior orbital fissure
Foramen rotundum
Foramen ovale
Foramen spinosum
Foramen
lacerum
Groove for greater
petrosal nerve
Groove for lesser
petrosal nerve

Posterior cranial fossa
Boundaries:
posterior clinoid process, upper border of
petrous temporal bone, groove for transvers
sinus, internal occipital protuberance
Bones to be identified;
• Basilar part of occipital bone, in
front of F magnum. Together with the
basilar part of sphenoid they form
the clivus.
• Condylar part of occipital bone,
on each side of F magnum.
• Squamous part of occipital bone,
behind F magnum.
• Posterior surface of petrous
temporal bone, lateral to the
occipital bone
• Mastoid part of temporal bone,
behind and lateral to the petrous
part.
Basilar part of
occipital bone
Basilar part
of sphenoid
Squamous part
of occipital bone
Petrous
temporal bone
Clivus
Condylar part
of occipital bone
Mastoid part
of temporal bone

Features of the posterior cranial fossa
• Internal occipital protuberance, a median
elevation on the squamous part of occipital bone
• Internal occipital crest, a median ridge
extending from the internal occipital
protuberance to the F. magnum
• Groove for transverse venous sinus, extends
from the internal occipital protuberance to the
mastoid part of temporal bone
• Sigmoid sulcus, an S-shaped sulcus extending
from the end of the groove for transverse sinus
to the jugular foramen
• Groove for superior petrosal sinus, running
along the upper border of petrous temporal bone
• Groove for inferior petrosal sinus, running
along the ptrosphenoidal fissure (between
petrous bone and occipital bone)
Internal occipital
protuberance
Internal occipital
crest
Groove for transverse
venous sinus
Sigmoid sulcus
Groove for superior
petrosal sinus
Groove for inferior
petrosal sinus

Foramina to be identified:
• Foramen magnum
• Jugular foramen, between the occipital
and petrous bones
• Hypoglossal canal, above the occipital
condyle
• Condylar canal, connects the codylar
fossa (seen on the norma basalis externa)
with the sigmoid sulcus
• Mastoid foramen, on the line of the
occipito-mastoid suture (opens into the
sigmoid sulcus)
• Internal acoustic meatus, on the
posterior surface of petrous bone
Foramen
magnum
Jugular foramen
Hypoglossal
canal
Condylar canal
Mastoid foramen
Internal acoustic
meatus
Foramen spinosum
Foramen ovale
Foramen
rotundum
Foramen
lacerum