Superficial face; scalp
Parotid region and deep face
Intracranial cavity; meninges
Eye and orbit
Oral cavity and contents
Ear and temporal bone
Introduction to the skull
Development of the skull
Base of skull: endochondral ossification
- Brain and cranial nerves develop before the skull, so when the chondrocranium
develops, its components form around the nerves and form foramina.
- The chondrocranium ossifies from a number of centers.
- The last piece of cartilage to ossify is between the body of the sphenoid
bone and the occipital bone, anterior to the foramen magnum: this is the
spheno-occipital synchondrosis (the epiphyseal plate for growth
in length of the base of the skull and it ossifies at age 25).
Bones of calvarium: intramembranous ossification
- The bones of the calvarium also ossify from separate centers and they
meet to form sutures. The process is completed at about 3 years.
Bones of the face are partly basal and partly calvarial bones so they
ossify both by intramembranous and endochondral ossification.
The bones of the cranium and the underlying lobes of the brain have the
- The frontal bone (which houses the frontal lobe of the brain)
ossifies from 2 centers and there are right and left frontal bones at birth.
The metopic suture separating the 2 normally ossifies leaving
one large frontal bone.
- The parietal bones are separated by the sagittal suture and
from the frontal bone by the coronal suture.
At birth, the anterior fontanelle (bregma) is a diamond-shaped
area between the 2 frontal bones and the 2 parietal bones. It pulsates
and bulges when the baby cries. It closes by 18 months to 2 years.
- The parietal bones and the occipital bone meet at the posterior
- The side wall of the skull is completed by the squamous part of
the temporal bone and the greater wing of the sphenoid bone,
at the pterion. It is located 4 cm above the midpoint of the zygomatic
arch and is the site of surgical exploration for the middle meningeal
- The flat bones of the skull (frontal, parietal, temporal and occipital)
are formed by a sandwich of diploë (cancellous bone containing
red bone marrow) between 2 layers of compact bone.
- The bones are drained by diploic veins (usually 4 on each side)
which open into the nearest convenient venous sinus.
- The flat bones of the skull are also pierced by emissary foramina
transmitting emissary veins connecting veins of the scalp with the
dural venous sinuses inside the skull (possible route for infection).
They may be seen in the parietal bone or in the temporal bone posterior
to the external auditory meatus.
In an X-ray of the skull, there is the need to differentiate the following
normal structures from fractures :
- the sutures (possible metopic suture),
- the diploic veins,
- and the middle meningeal artery.
The pineal gland near the center of the brain may contain corpora
aranaceae (calcareous granules) and it can be used to detect displacement
of the brain.
- The occipital bone: the external occipital protuberance
is located inferior to lambda. The superior nuchal lines run lateral
from the external occipital protuberance and the inferior nuchal lines
are situated inferiorly.
THE CRANIAL FOSSAE: 3 fossae forming 3 steps down to foramen
magnum from front to back.
1) Anterior cranial fossa:
- Orbital plate of the frontal bone
- Lesser wing of the sphenoid bone
- The cribriform plate of the ethmoid with the crista galli transmits
olfactory nerves from the upper part of the nasal cavity; this is a possible
route for infection or escape route for CSF in skull fractures.
- Optic canal for transmission of optic nerve.
- Anterior clinoid processes projecting posteriorly to the posterior
clinoid processes of the sphenoid bone.
2) Middle cranial fossa
- is formed by the greater wing of the sphenoid bone and the temporal
bone. It is occupied by the temporal lobe of the brain.
- The greater wings and the body of the sphenoid bone form a butterfly
- The most posterior tip of the greater wing contains the foramen
- Anteriorly to the foramen spinosum is the foramen ovale and
then the foramen rotundum. The foramen rotundum leads to the pterygopalatine
- The superior orbital fissure is a gap between the lesser wing
and the greater wing of the sphenoid leading to the orbit, just lateral
to and below the optic nerve.
- The body of the sphenoid bone contains the hypophyseal fossa
for the pituitary gland. This fossa is also called the sella turcica
and it is shaped like a 4-poster bed (clinoid processes; clinical = patient
is in bed). Its maximum length is 14mm and its depth is 8mm. Measurements
are important because pituitary tumors cause ballooning of the sella.
- The foramen lacerum is located lateroposterior to the sella.
The middle meningeal artery enters the skull through the foramen
spinosum and its groove can be traced laterally and anteriorly on the squamous
portion of the temporal bone before dividing into anterior and posterior
(frontal and parietal) branches.
- The anterior branch crosses the greater wing at the pterion and then
breaks up into branches that run superiorly and posteriorly.
- The posterior branch runs posteriorly supplying bone and meninges.
3) Posterior cranial fossa
- is formed by the temporal bone and the occipital bones.
- houses the cerebellum.
The posterior cranial fossa contains:
- the foramen magnum for the lower end of the medulla.
- The clivus, anterior to the foramen magnum, which leads up to
the body of the sphenoid bone.
- The transverse sinus
- The sigmoid sinus which ends at the jugular foramen.
- The hypoglossal canal (anterior condylar) canal and the posterior
- The internal auditory meatus on the posterior aspect of petrous
- The arcuate eminence on the petrous portion of the temporal
bone, marking the position of the superior semicircular canal.
The superior sagittal sinus is continuous with the right transverse
sinus whereas the smaller straight sinus is continuous with the
left transverse sinus. The right jugular foramen is thus usually larger
than the left.
THE EXTERIOR OF THE BASE OF THE SKULL
- Recognize the above- mentioned foramina from the exterior.
- The spine of the sphenoid bone near the foramen spinosum.
- The jugular foramen is occupied by the jugular bulb (for expansion
of the internal jugular vein) in life.
- The styloid process, the mastoid process and the stylomastoid foramen
between the 2 processes.
- Anterior to the jugular foramen and in the petrous portion of the temporal
bone lies the carotid canal.
- The spine of the sphenoid bone lies medial to the mandibular fossa.
The mandibular fossa articulates with the head of the mandible to form
the temporomandibular (TMJ) joint.
- The foramen ovale lies at the base of the lateral pterygoid
- The medial pterygoid plate (with the pterygoid hamulus
at its base) and the lateral pterygoid plate are parts of the sphenoid
- The inferior orbital fissure leads anteriorly from the pterygoid
region to the orbit.
- The hard palate is formed by the palatine process of the
maxilla and by the horizontal plate of the palatine bone. There
are 3 foramina in the horizontal plate, the larger being the greater
- The vomer bone in the posterior opening (the choanae)
of the nasal cavity is attached by a fibrous joint to the undersurface
of the body of the sphenoid.
The internal carotid artery:
- enters the carotid canal,
- runs anteromedially to the foramen lacerum
- and then runs superoanteriorly to enter the cranium through the internal
orifice of the foramen lacerum.
- It then turns anteriorly and lies on the side of the sella turcica.
It now lies in the cavernous sinus.
- It then turns superoposteriorly, medial to the anterior clinoid process
and breaks up into 3 branches.
THE SKELETON OF THE FACE
In the orbit are found:
- the superior orbital fissure
- the optic canal
- The greater and lesser wings of the sphenoid.
- The zygomatic bone and the (hollow) maxilla are in the lateral
wall of the orbit.
- The ethmoid bone and the small fragile lacrimal bone
are in the medial wall .
The supraorbital, infraorbital and mental foramina, lie on a vertical
line and transmit the ophthalmic, maxillary and mandibular divisions
of the trigeminal (Vth cranial) nerve.