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The Gross Anatomy
of the Head:
The skull
Philip A. ADENIYI
Cell Biology and Neurotoxicity Unit,
Department of Anatomy,
Afe Babalola University Ado-Ekiti (ABUAD),
Nigeria
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THE HEAD
Osteology of the skull
Introduction:
• superior part of the body that is attached to the trunk by the neck
Composition:
• the brain and its protective coverings, the ears, and the face
The Cranium
Introduction:
• The cranium (skull) is the skeleton of the head
• The many bones of the head collectively form the skull
• Most of these bones are interconnected by sutures which are
immovable fibrous joints
Parts:
• has two parts:
the neurocranium /cranial vault
the viscerocranium/ facial skeleton
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Neurocranium (Cranial vault)
Introduction:
• is the bony covering (case) of the brain and its membranous
coverings, the cranial meninges
• It also contains proximal parts of the cranial nerves and the
vasculature of the brain
Parts:
The neurocranium has;
• a dome-like roof called the calvaria (skullcap)
• and a floor or cranial base (basicranium)
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Composition:
• The neurocranium in adults is formed by a series of eight
bones:
Four are singular bones
and the other two sets of bones occur as bilateral pairs
The four singular bones are:
frontal
ethmoidal
sphenoidal
occipital
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• While two sets of bones occurring as bilateral pairs are:
Temporal
parietal
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The ethmoid bone is an irregular bone that makes a relatively
minor midline contribution to the neurocranium but is primarily
part of the viscerocranium
Viscerocranium (facial skeleton)
• comprises the facial bones
• forms the anterior part of the cranium
• consists of the bones surrounding the mouth (upper and lower
jaws), nose/nasal cavity, and most of the orbits (eye sockets or
orbital cavities)
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Composition:
• consists of 15 irregular bones:
• Three are singular bones
• While 6 bones occur as bilateral pairs
The three singuar bones are:
Mandible
Ethmoid
Vomer
The 6 bilateral paired bones are:
Maxillae
inferior nasal conchae
zygomatic
palatine
nasal
lacrimal bones
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Note:
• The maxillae and mandible house the teeths
• They provide the sockets and supporting bone for the maxillary
and mandibular teeth.
• The Maxillae:
contribute the greatest part of the upper facial skeleton,
form the skeleton of the upper jaw
It is fixed to the cranial base
• The Mandible :
forms the skeleton of the lower jaw,
It is movable because it articulates with the cranial base at the
temporomandibular joints (TMJs)
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Anterior or facial(frontal) aspect of the Cranium
Features include:
the frontal bone
zygomatic bones
orbits
nasal region
maxillae
mandible
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The frontal bone
it is a squamous (flat) part
forms the skeleton of the forehead
articulates inferiorly with the nasal and zygomatic bones.
The supraorbital margin of the frontal bone has a supraorbital
foramen (notch) for the passage of the supraorbital vessels and
nerves
Just superior to the supraorbital margin is a ridge called the
superciliary arch
Between these arches is a smooth, slightly depressed area called the
GLABELLA
The Glabella is the anterior most projecting part of the forehead
Just above the glabella is a point on the midline of the forehead
called the Ophyron
On the midline of the mandible is the the most anterior point on the
mandible which is the most prominent part of the chin.
This point is called the pogonion
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• The intersection of the frontal and nasal bones is called the NASION,
a depressed area (bridge of the nose)
• The frontal bone also articulates with the lacrimal, ethmoid, and
sphenoids bones
The nasal region
• made up of a pair of nasal bones which are joined together at midline
by the nasal septum
• Inferior to these nasal bones is a pear shaped piriform aperture
• the bony nasal septum can be observed through this aperture dividing
the nasal cavity into the right and left parts
• On the lateral wall of each nasal cavity are curved bony plates called
the nasal conchae
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Maxillae
• form the skeleton of the upper jaw
• Occur in pairs
• The two maxillae are united at the intermaxillary suture in the
median plane
• their alveolar processes include the tooth sockets (alveoli) and house
the maxillary teeth
• They articulate with the frontal bone anteriorly and zygomatic bones
laterally
• On the body of the maxilla is the infraorbital foramen for passage of
the infraorbital nerve and vessels
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Mandible
• is a U-shaped bone
• forms the skeleton of the lower jaw
• Its alveolar process supports the mandibular teeth.
consists of:
of a horizontal part (the body)
and a vertical part (the ramus )
• Inferior to the second premolar teeth are the mental foramina for
the passage of the mental nerves and vessels
• The base of the mandible has a midline swelling called the mental
protuberance
• Lateral to the mental protuberance on either side is a slightly more
pronounced bumps called the mental tubercles
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Zygomatic Bone
• Also known as cheek bone, malar bones
• On the lateral aspect of this bone is a foramen called the
zygomaticofacial foramen
• this foramen allows for the passage of the zygomaticofacial nerve
• This bone articulates with the frontal, sphenoidal, maxillae and
temporal bones
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Clinical anatomy
Injury to the superciliary arches
• The superciliary arches are relatively sharp bony ridges;
consequently, a blow to them (e.g., during boxing) may lacerate the
skin and cause bleeding. Bruising of the skin surrounding the orbit
causes tissue fluid and blood to accumulate in the surrounding
connective tissue, which gravitates into the superior (upper) eyelid
and around the eye
Malar Flush
• The zygomatic bone was once called the malar bone.
• Clinically the term malar flush refers to redness of the skin
covering the zygomatic prominence (malar eminence), which is
associated with a rise in temperature in various fevers occurring
with certain diseases, such as tuberculosis
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Superior aspect of the skull
Also called the calvaria or skull cap
Bones forming it include
Frontal bone (unpaired)
Paired parietal bones
Occipital bone (unpaired)
The outer surface of the skull possess a number of landmarks
The frontal bone articulates with the paired parietal bones at the
coronal suture
The two parietal bones articulate with each other at the sagittal
suture
The paired parietal bones articulate with the occipital bones at the
lambdoid suture
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The junction(intersection) between the coronal and sagittal sutures
is called the bregma
The junction (intersection) between the sagittal suture and
lambdoid sutures is called the lambda
The vertex is the most superior point of the skull near the midpoint
of the sagittal suture
The parietal foramen on the parietal bone is variable, and it
allows for the passage of emissary veins
Obelion: The region of the skull between the two parietal foramina
where the closure of the sagittal suture usually begins
Clinical Anatomy
Fracture of the Calvaria
Depressed fractures:
this can results from hard blows in thin areas of the calvaria in
which a bone fragment is depressed inward, compressing and/or
injuring the brain
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Linear calvarial fractures :
the most frequent type
usually occur at the point of impact; but fracture lines often radiate
away from it in two or more directions
Comminuted fractures:
the bone is broken into several pieces
If the area of the calvaria is thick at the site of impact, the bone may
bend inward without fracturing; however, a fracture may occur some
distance from the site of direct trauma where the calvaria is thinner
Contrecoup (counterblow) fracture:
no fracture occurs at the point of impact, but one occurs on the
opposite side of the cranium
Obliteration of the Cranial Sutures
• The obliteration of sutures between the bones of the calvaria usually
begins between the ages of 30 and 40 years on the internal surface
and approximately 10 years later on the external surface
• Obliteration of sutures usually begins at the bregma and continues
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sequentially in the sagittal, coronal, and lambdoid sutures
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Skull of a newborn baby
The halves of the frontal bone in the newborn are separated by the
frontal suture
the frontal and parietal bones are separated by the coronal suture
and the maxillae are separated by the intermaxillary suture
mandible consists of two halves united in the median plane by the
mandibular symphysis
this union begins during the 1st year and the halves are fused by the
end of the 2nd year
No mastoid process at birth
No styloid process
The mastoid processes form gradually during the 1st year
The bones of the calvaria of a neonate are separated by membranous
intervals called frontanelles
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They include:
anterior fontanelle
posterior fontanelle
paired sphenoidal fontanelle
Paired mastoid fontanelles
Anterior fontanelle
intro: the largest frontanelle
shape: diamond or star shaped
boundary: bounded by the halves of the frontal bone anteriorly and the
parietal bones posteriorly.
Location: at the junction of the sagittal, coronal, and frontal sutures, the
future site of the bregma
closure: By the 18 months of age, the surrounding bones have fused and the
anterior fontanelle is no longer clinically palpable
Frontal bone of a newborn
Union of the halves of the frontal bone begins in the 2nd year
In most cases, the frontal suture is obliterated by the 8th year
in approximately 8% of people, a remnant of the frontal suture persist called
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the metopic suture
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Posterior fontanelle
• Shape: is triangular
• boundary: bounded by the parietal bones anteriorly and the occipital
bone posteriorly
• location: at the junction of the lambdoid and sagittal sutures, the
future site of lambda
• Closure: begins to close during the first few months after birth and by
the end of the 1st year, it is small and no longer clinically palpable
Sphenoidal and mastoid fontanelles
• overlain by the temporal muscle,
• fuse during infancy and are less important clinically than the midline
fontanelles
note
• The halves of the mandible fuse early in the 2nd year
• The two maxillae and nasal bones usually do not fuse
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Molding of the calvaria
The softness of the cranial bones in infants and their loose connections at
the sutures and fontanelles enable the shape of the calvaria to change
(mold) during birth
During passage of the fetus through the birth canal, the halves of the
frontal bone become flat, the occipital bone is drawn out, and one
parietal bone slightly overrides the other
Within a few days after birth, the shape of the calvaria returns to normal
The resilience of the cranial bones of infants allows them to resist
forces that would produce fractures in adults
The fibrous sutures of the calvaria also permit the cranium to enlarge
during infancy and childhood
The increase in the size of the calvaria is greatest during the first 2 years,
the period of most rapid brain development
The calvaria normally increases in capacity for 15-16 years
After this, the calvaria usually increases slightly in size for 3-4 years as a
result of bone thickening
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Craniosynostosis and Cranial Malformations
• Premature closure of the cranial sutures is called craniosynostosis
results in several cranial malformations
• Premature closure of the sagittal suture, in which the anterior
fontanelle is small or absent, results in a long, narrow, wedgeshaped cranium, a condition called scaphocephaly
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When premature closure of the coronal or the lambdoid suture
occurs on one side only, the cranium is a condition known as
plagiocephaly
• Premature closure of the coronal suture results in a high, tower-like
cranium, called oxycephaly or turricephaly
• oxycephaly or turricephaly is more common in females
Note: Premature closure of sutures usually does not affect brain
development
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Lateral aspect of the skull
This includes :
lateral part of the neurocranium
Lateral part of the viscerocranium (facial skeleton)
Composition:
• bones forming the lateral portion of the neurocranium include: the
frontal, parietal, occipital, sphenoid, and temporal bones
• bones forming the visible part of the facial skeleton include the nasal,
maxilla, and zygomatic bones and the mandible
• The main features of the neurocranial part are the temporal fossa, the
external acoustic opening, and the mastoid process of the temporal
bone
• The main features of the viscerocranial part are the infratemporal
fossa, zygomatic arch, and lateral aspects of the maxilla and mandible
The junction where the frontal, parietal, sphenoid(greater wing) and
temporal bone meet is called the pterion
• It is usually indicated by an H-shaped formation of sutures
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Clinical anatomy
• The pterion is an important area because it overlies the middle
meningeal artery
• Fracture to the pterion can rupture the anterior branch of this artery
resulting in hematoma which exerts pressure on the underlying
cerebral cortex
• An untreated meningeal artery can cause hemorrhage which can lead
to death in a few hours
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• In the anatomical position, the cranium is oriented in such a way that
the inferior margin of the orbit and the superior margin of the
external acoustic meatus opening of both sides lie in the same
horizontal plane
• This standard craniometric reference/ plane is called the
orbitomeatal plane (Frankfort horizontal plane)
The temporal bone of the lateral aspect of the skull
It has:
a squamous part which articulates with the greater wing of sphenoid
at the sphenosquamous suture
a zygomatic process which articulates with the zygomatic bone to
form the zygomatic arch
a tympanic part which has the external acoustic meatus
a petromastoid part which is usually separated into the petrous and
mastoid part
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• A large bony prominence projects from the inferior border of the
mastoid part of the temporal bone called the mastoid process
• Medial to the mastoid process is the styloid process which projects
from the lower border of the temporal bone
• The point where the superior temporal line cuts the coronal suture is
called the stephanion
• While the located at junction of three sutures: parietomastoid,
occipitomastoid, and lambdoid is called the asterion
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Posterior aspect of the skull
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Bones include:
• Occipital bone
• Parts of the parietal bones
• Temporal bones (mastoid part)
Occipital bone
The occipital bone is separated from the paired parietal bone by the
lambdoid suture
Along the lambdoid suture are small bones called sutural or wormian
bones
there is a midline projection called the external occipital
protuberance
Curved lines extend laterally from this projection called the superior
nuchal lines
The most prominent part of the external occipital protuberance is the
inion
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About 1 inch (2.5cm) below the nuchal lines are additional 2 lines
called the inferior nuchal lines which curves laterally
Extending downwards from the external occipital protuberance is the
external occipital crest
In between the mastoid and the occipital in is the occipitomastoid
suture
Note
Obliteration of Cranial Sutures
• The obliteration of sutures between the bones of the calvaria usually
begins between the ages of 30 and 40 years on the internal surface
and approximately 10 years later on the external surface
• Obliteration of sutures usually begins at bregma and continues
sequentially in the sagittal, coronal, and lambdoid sutures
The region of the skull between the 2 parietal foramina where the
closure of the sagittal suture begins is called the OBELION
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The Internal surface of the cranial base (cranial cavity/fossae)
• has three large depressions that lie at 3 different levels:
anterior crania fossa
middle cranial fossa
posterior cranial fossa
• These form the bowl-shaped floor of the cranial cavity
• The anterior cranial fossa is at the highest level(shallowest)
• while the posterior cranial fossa is at the lowest level(deepest)
Sitting on the floor of the anterior cranial fossa is the frontal lobes
of the cerebral hemisheres
Sitting on the floor of the lateral portion of the middle cranial fossa
is the temporal lobe, and in the midline of the middle crania fossa
is the pituitary gland
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Sitting on the anterior portion of the floor of the posterior cranial
fossa is the brainstem (midbrain, pons and medulla oblongata)
and occupying the rest of the posterior cranial fossa are the
cerebellar hemispheres
Note: the occipital lobe do not sit on the floor of the posterior
cranial fossa, it is the cerebellum that sit of the floor of the
posterior cranial fossa
Anterior cranial fossa
Introduction:
• Shallowest of the 3 cranial fossae
• Lodges the frontal lobe of the brain
Bony formation:
• Formed by 3 bones, namely:
Frontal bone in the anterior and lateral directions
Ethmoid bone in the middle portion
2 parts of the sphenoid bone in the posterior portion
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• The part of the frontal bone in the anterior cranial fossa is the
orbital part/orbital surface
• The ethmoid bone of the anterior cranial fossa is made up of :
A ridge which projects superiorly called the crista galli
And a sieve- like cribriform plate of ethmoid which lies on each
sides of this ridge
• The 2 parts of the sphenoid bone in the anterior cranial fossa are:
The jugum
The lesser wing of sphenoid
Foramen
The cribriform plate of ethmoid has numerous tiny foramina that
transmit olfactory nerves (CN 1) from the olfactory area of the
nasal cavity to the olfactory bulb of the brain
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• The frontal bone also has a bony median extension called the frontal
crest, at the base of the frontal crest is the foramen cecum
• This foramen varies in size in different individuals, and is frequently
impervious; when open, it transmits the emissary vein from the nose to
the superior sagittal sinus
• This has clinical importance in that infections of the nose and nearby
areas can be transmitted to the meninges and brain
• Each lesser wing widens, curves posteriorly, and ends as a rounded
anterior clinoid process
• Just anterior to each anterior clinoid process is a circular opening in
the lesser wing of the sphenoid called the optic canal
• The optic canal allows for the passage of
ophthalmic artery and
optic nerve [CN II] to pass through as they exit the cranial cavity to
enter the orbit
Note: The optic canals are usually included in the middle cranial fossa
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Middle crania fossa
• It is butterfly shaped
separating the anterior and middle cranial fossae are the sharp
sphenoidal crests laterally and the sphenoid limbus centrally
The sphenoid limbus forms the posterior boundary of the jugum and
the anterior boundary of the prechiasmatic sulcus
(note:the prechiasmatic sulcus is bounded posteriorly by the
tuberculum sellae)
The prechiasmatic sulcus is a smooth groove stretching between the
optic canals across the body of the sphenoid
Bony formation
• Formed mainly by the:
i. Parts of the sphenoid bone
ii. Parts of the temporal bone
The parts of sphenoid involved are:
i. Sella turcica which is part of the body of sphenoid
ii. greater wings of sphenoid laterally
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Sella turcica
• Has 3 parts:
i. an anterior wall called the turberculum sella
ii. a posterior wall called the dorsum sella
iii. a deep central part lying in between the turberculum sella and
dorsum sella
This central part is called the hypophyseal fossa, which houses the
pituitary gland
• On each side of the body of the sphenoid are four foramina
perforating the roots of the greater wings of the sphenoid, these
include :
i. Superior orbital fissure: a diagonal gap that separates the greater
wing from the lesser wing of sphenoid
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• This fissure allows for the passage of the:
Cranial nerves III, IV and VI (occuomotor, trochlear and
abducens nerves)
Ophthalmic division of trigerminal nerve (CN V1)
ophthalmic vein
ii foramen rotundum: allows for the passage of the maxillary
division of the trigeminal nerve (CN V2)
iii foramen ovale: allows for the passage of the mandibular division
of the trigeminal nerve (CN V3)
iv foramen spinosum: allows for the passage of the middle
meningeal artery and the meningeal branch of mandibular nerve
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Parts of the temporal bone include:
squamous part of the temporal bones laterally
and the petrous part of the temporal bones posteriorly
On the petrous part are grooves for both the greater and lesser petrosal
nerves
Posterolateral to the hypophyseal fossa is the foramen lacerum
(lacerated or torn foramen) is not part of the crescent of foramina and is
an artifact of a dried cranium
In life, it is closed by a cartilage plate
Only some meningeal arterial branches and small veins are
transmitted vertically through the cartilage completely traversing this
foramen
The lateral parts of the middle cranial fossa support the temporal lobes
of the brain
The boundary between the middle and the posterior cranial fossae is the:
superior border of the petrous part of the temporal bone laterally
and a flat plate of bone, the dorsum sellae of the sphenoid, medially 66
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Posterior cranial fossa
Largest and deepest of the 3 cranial fossa
Lodges the brainstem (medulla oblongata, pons and midbrain) and
the cerebellum
Formed mainly by the occipital bone and the temporal bone
There is a slope that extend down from the dorsum sellae leading to
the foramen magnum called the clivus
posterior to the foramen magnum are cerebellar fossae which
accommodate the cerebellar hemispheres
The cerebellar fossae are partly divided by the internal occipital crest
into bilateral concave impression
The internal occipital crest ends superiorly in a bony prominence
called the internal occipital protuberance
At the base of the petrous ridge of the temporal bone is the jugular
foramen
Anterosuperior to the jugular foramen is the internal acoustic meatus
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Grooves and foramen in the posterior cranial fossa
• internal acoustic meatus: passage of facial nerve (CN VII) and
vestibulochear nerve (CN VIII) and the labyrinthine artery
• Jugular foramen: allows the passage of:
3 cranial nerves pass through it, which are cranial nerves IX, X
and XI {glossopharyngeal,vagus and accessory nerve}
2 important venous structures, the dura venous sinuses, coming in
from the posterior side is the sigmoid sinus and from the anterior
side is the inferior petrosal sinus
Note: these two sinuses enter the jugular foramen and when they
emerge from the other side, they fuse together and once fused
together, they are called the internal jugular vein
• hypoglossal canal: located superior to the anterolateral margin
of the foramen magnum and allows for the passage of the
hypoglossal nerve {CN XII}
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• Foramen magnum: allows for the passage of;
The spinal cord which is continuous with the medullar
obongata
The two vertebral arteries
The spinal contribution of accessory nerve, the spinal
accessory nerve
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External aspect of cranial base
The base of the skull is seen in the inferior view and extends
anteriorly from the middle incisor teeth, posteriorly to the
superior nuchal lines and laterally to the mastoid processes and
zygomatic arches
For descriptive purposes the base of the skull is often divided
into:
an anterior part, which includes the teeth and the hard palate;
a middle part, which extends from behind the hard palate to
the anterior margin of the foramen magnum;
a posterior part, which extends from the anterior edge of the
foramen magnum to the superior nuchal lines
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Anterior part
The main features are:
The teeth project from the alveolar arches of the two maxillae
• These arches are arranged in a U-shaped configuration that
borders the hard palate on three sides
The hard palate is composed of the palatine processes of each
maxilla anteriorly and the horizontal plates of each palatine
bone posteriorly
• The paired palatine processes of each maxilla meet in the
midline at the intermaxillary suture
• and the paired horizontal plates of each palatine bone meet in
the midline at the interpalatine suture
• the paired maxilla and the paired palatine bones meet at the
palatomaxillary suture
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Several additional features are also visible when the hard palate
is examined:
• the incisive fossa for the passage of nasoplatine and
sphenopalatine vessels
• the greater palatine foramina for the passage of greater
palatine vessels and nerve
• just posterior to the greater palatine foramina is the lesser
palatine foramina for the passage of lesser palatine vessels
and nerve
• a midline pointed projection in the free posterior border of the
hard palate called the posterior nasal spine
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Middle part
• The middle part of the base of the skull is complex:
forming the anterior half are the vomer and sphenoid bones;
forming the posterior half are the occipital and paired temporal
bones.
Anterior half
Vomer
• Anteriorly, the small vomer is in the midline, resting on the
sphenoid bone
• It contributes to the formation of the bony nasal septum separating
the two choanae
Sphenoid
Only 3 parts of the spheniod is seen in the inferior view
They are:
• body
• Greater wings
• 2 pterygoid processes on each side
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• The pterygoid process consist of a medial plate and a lateral plate
separated by the pterygoid fossa
The body:
• It articulates anteriorly with the vomer, ethmoid, and posterolaterally
with the temporal bones, and posteriorly with the occipital bone
The greater wing:
• Articulates laterally and posteriorly with the temporal bone
Important features on the greater wing are:
Foramen ovale: passage of mandibular nerve (V3)
Foramen spinosum: passage of middle meningeal artery
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Posterior half
Made up of
• Part of Occipital bone
• Parts of paired temporal bones
Occipital bone
• This include the basilar part of the occipital bone, which is posterior
to the body of sphenoid
• posterior to this part is the foramen magnum and it is bounded
laterally by the temporal bone
• Prominent structure on the basilar part is the pharygeal tubercle
Temporal bone
Has a rough petrous part
• Features here include:
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Carotid canal for the passage of internal carotid artery
Mandibular fossa for the head of the mandible (condylar process)
External acoustic meatus
Styloid process
Posterior part
• Extend from the anterior edge of foramen magnum to the superior
nuchal line posteriorly
• Consist of the occipital bone in the central and posterior part and
the temporal bone laterally
Features on the occipital bone
1. Jugular notch: present in the temporal bone for the passage of
Cranial nerve IX to XI
Internal jugular vein
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2.
Foramen magnum located in the occipital bone for the passage of:
The spinal cord which is continuous with the medullar oblongata
The two vertebral arteries
The spinal contribution of accessory nerve, the spinal accessory
nerve
3. Occipital condyles: located on each side on the anterolateral
margin of the foramen magnum for articulation with the atlas (the
1st cervical verterbra)
Features on the temporal bone:
• Mastoid process
between the base of the styloid process and the mastoid process is
the stylomastoid foramen
• This foramen allows for the passage of the facial nerve (CN VII)
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