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11/10/2016
Anatomy #10
Skull
Nour Erekat
Farah Behari
Views of the skull
Objectives:
 Describe the anterior and posterior views of skull both internally and
externally
 Describe the lateral view of skull both internally and externally
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Describe the superior and inferior views of skull both internally and
externally
 Describe the base of the skull and its major foramina as well as the
structures that pass through them
The skull is made up of bones that are grouped into two groups based
on the overall structure that they participate in forming. One group
consists of the bones that form the cranium (neurocranium). The
cranium is the cavity that houses the brain, its different meninges and
blood vessels. The other group consists of bones that form the face
called facial bones.
All cranial bones (frontal,
occipital, sphenoid and ethmoid)
are single-unpaired, except for two,
the parietal and temporal bones.
Regarding the facial bones, they
are the exact opposite of the cranial
bones, 2 are unpaired or single (the
mandible and vomer) whereas all
the others (nasal, maxillae,
zygomatic, lacrimal, palatine,
inferior nasal conchae) are paired.
Anterior view of the skull
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The blue bone is the frontal bone
There are 2 orbits; each orbit is a cavity called the eye socket and contains the
eyeball.
The supraorbital margin of the orbit is formed by the frontal bone
At the medial third of the supraorbital margin , there is the supraorbital
foramen(canal)
Supraorbital ridge
 just above the supraorbital margin there is a ridge
called the supraorbital ridge (also called superciliary arch
or brow ridge), and in between the two ridges is a flattened
part of the frontal bone called the glabella
Glabella
The frontal air sinuses (one group of the paranasal sinuses)
lie deep within the frontal bone, specifically deep to the
superciliary ridges. “Sinus≡ airspace”
The yellow colored bone is the maxilla. 2 maxillae form the
upper jaw. The frontal process of the maxilla ascends upward
to articulate with the frontal bone; thereby it’s called the
frontal process of the maxilla. Each maxilla exhibits a frontal
process so we have two frontal processes of the maxillae.
Below the inferior margin of the orbit there is a foramen
perforating each maxilla called the infraorbital (below the
orbit) foramen. The alveolar arch is the part of the maxilla
that descends projecting forward and craving the roots of the
different teeth; it is formed by the alveolar processes of the
two maxillae. The two maxillae join and articulate in the midline at the intermaxillary
(between the two maxillae) suture.
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The anterior nasal apertures (heart shaped opening) are formed by the lower
borders of the nasal bones above and the maxillae below.
There are 3 pairs of conchae which are just moony shelves
projecting from the lateral wall of the nasal cavity
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the superior nasal conchae
the middle nasal conchae
Both middle and superior nasal conchae are part of the
ethmoid bone, specifically the lateral mass of the ethmoid
bone.
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The inferior nasal conchae, which are separate
facial bones or entities.
The nasal cavity is divided into two halves by the nasal
septum which is an osteocartilagenous structure. There are
two bony parts forming the nasal septum, the perpendicular
or vertical plate of the ethmoid bone anteriosuperiorly and
the vomer posteroinferiorly.
The mandible is mainly divided into:
The body of the mandible which has 2 major foramina adjacent to
the second premolar teeth and the vertical rami
The orange colored bones in the first figure are the zygomatic bones.
The zygomatic bone produces the prominence of the cheek. There are
two foramina in the zygomatic bone, the zygomaticofacial and the
zygomaticotemporal foramina, which are named according to the
nerves that they transmit (zygomaticofacial and zygomaticotemporal
nerves). The zygomatic bone articulates medially with the maxilla and
laterally with the temporal bone.
Bridge of the
nose
This is the image of a real or plastic skull; you must recognize the following:
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The part of the
zygomatic arch formed
by the temporal
process of the
zygomatic bone
the frontal bone articulating with the two nasal bones that form the bridge of the
nose
the anterior nasal apertures leaving into the two halves of the nasal cavity and the
septum dividing between them
the middle nasal concha which is part of the ethmoid bone and the inferior nasal
concha which is a fascial bone
2 maxillae meeting at the intramaxillary suture
2 zygomatic bones and the small part of the zygomatic arch formed by the
temporal process of the zygomatic bone
the mandible’s horizontal body and two vertical rami
Lateral view of the skull
The anterosuperior part of the skull if formed by the frontal bone (single-unpaired); the
parietal bones (paired) lie posterior to the frontal bone.
The parietal bone articulates with the
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frontal bone at the coronal suture
occipital bone posteriorly at the lambdoid suture
other parietal bone superiorly in the midline at the sagittal suture
The zygomatic bone is articulating with the frontal bone superiorly, maxillae medially
and zygomatic process of the temporal bone laterally to form the zygomatic arch.
The purple colored bone is the temporal bone which has the following main parts:
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the temporal squama which is the flat part of the bone
the tympanic part that forms the bony part of the auditory tube
the styloid process which is the narrow slender process projecting downwards
the mastoid process posteriorly
the external auditory meatus
The mandible:
Notice the mandibular notch which separates the
coronoid process anteriorly and condylar process
posteriorly. The condylar process consists of the
head (above the neck) and the neck.
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The green colored bone is the greater wing of the
sphenoid
The pterion of the skull is the thinnest and
weakest area of the lateral side of the skull.
It is where the anteroinferior corner of the
parietal bone articulates with the greater
wing of the sphenoid. It can also be thought
of as the site of articulation of the frontal
bone, temporal, parietal, and greater wing of
the sphenoid. This area is potential for
fractures as it is the weakest area of the
skull. The most important point regarding
the pterion is that it overlies the anterior division of the middle meningeal artery (a
branch of the maxillary artery), so whenever the skull is traumatized laterally resulting in
a fracture, the middle meningeal artery ruptures leading to epidural hematoma.
Posterior
margin of
the
zygomatic
process
Zygomatic
process of
the
frontal
bone
The different parts of the temporal bone as seen laterally:
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Zygomatic process of the temporal bone articulating with the temporal process of
the zygomatic bone forming the zygomatic arch
Temporal squama
Tympanic plate
Mastoid and styloid processes
From the posterior margin of the zygomatic process of the frontal bone temporal lines
begin and diverge as they arch backward forming two lines, the superior temporal line
and the inferior temporal line. Below the inferior temporal line, there is a depression
called the temporal fossa. The temporal fossa contains the pterion.
The part of the
greater wing of the
sphenoid below the
temporal fossa is
called the
infratemporal
crest of the
greater wing of
the sphenoid.
Below the
infratemporal crest
there is the
infratemporal
fossa. In the medial
wall of the
infratemporal fossa
is a downward projecting process of the greater wing of the sphenoid called the
pterygoid process; it lies posterior to the maxilla, in between there is a fissure called the
pterygomaxillary fissure. Medial to this fissure is the pterygopalatine fossa. (So it can
be thought of this way: the pterygomaxillary fissure is the lateral gate or door leading into
the pterygopalatine fossa medially.)
In the medial wall of the pterygopalatine fossa is a foramen called the sphenopalatine
foramen which is the communication between the pterygopalatine fossa and nasal cavity
medially. The pterygopalatine fossa is located below the apex of the orbit and posterior to
it so you expect it to communicate with the orbit anteriorly to the inferior orbital fissure,
now superiorly the sphenopalatine fossa articulates with the medial cranial fossa so the
cranial cavity through a foramen called foramen rotundum.
Posterior view of the skull
The parietal bones articulate with each other in the midline at the sagittal suture and
articulate with the posterior occipital bone at the lambdoid suture. The different parts of
the occipital bone as seen posteriorly in the midline are:
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The external occipital protuberance; which is a roughened elevation (prominence)
The 2 superior nuchal lines; which extend laterally on either side of the external
occipital protuberance towards the temporal bones.
The 2 inferior nuchal lines; which are parallel to the superior nuchal lines.
Superior view of the skull
Whenever you dissect a cadaver using an electric saw you remove the upper part of the
skull called the calvarium (calvaria)
The calvarium is made up anteriorly of the frontal bone which articulates with the two
parietal bones at the coronal suture, and posteriorly of the two parietal bones that
articulate at the sagittal suture.
Occasionally, the two halves of the frontal bones fail to fuse leaving a midline metopic
suture.
Inferior view of the skull
Posterior
nasal
aperture
The hard palate lies anteriorly. The hard palate is formed by the palatine process of the
maxillae anteriorly and the horizontal plate of the palatine bone
posteriorly. In the midline anteriorly, there is the incisive
foramen and posterolaterally there are the greater and lesser
palatine foramina.
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The two choanae or posterior nasal apertures are located above the posterior
edge of the hard palate; they are the site of communication between the nasal
cavity and the nasopharynx. These choanae are bordered by the vomer medially,
and by the medial pterygoid plate of the sphenoid bone. (Explanation of the
pterygoid plate: From the greater wing of the sphenoid projects a downward
process called the pterygoid process; the pterygoid process consists of two plates,
the medial pterygoid plate and the lateral pterygoid plate)
The inferior end of the pterygoid plate is prolonged forming the pterygoid
hamulus.
Posterolateral to the lateral pterygoid plate is the large oval-shaped foramen called
foramen ovale. Posterolateral to the foramen ovale is the foramen spinosoum.
Posterolateral to the foramen spinosoum is a small prominence projecting
downwards which is the spine of the sphenoid.
Anterolaterally on the temporal bone is the mandibular fossa.
Anterior to the mandibular fossa there is an articular tubercle. These two
structures form the upper articulating surfaces or temporomandibular joint.
Posterior to the mandibular fossa is the external auditory meatus and the tympanic
plate that forms the bony part of the external auditory meatus.
The tympanic plate of the temporal bone has the supranatal crest in the lateral
surface of the squamous part of the temporal bone as well as the supranatal
triangle and supranatal spine.
The squamotympanic fissure separates between tympanic plate posteriorly and
the mandibular fossa anteriorly. The medial end of the squamotympanic fissure
called the tympani exits or leaves the tympanic cavity.
The styloid process:
medial to the styloid process is a rocky Portion of the temporal bone called the petrous
part of the temporal bone. In the inferior surface of the petrous portion is an opening of
the carotid canal called the carotid foramen through which the internal carotid artery
passes. At the medial end of the petrous part of the temporal bone is a foramen called
foramen lacerum.
The foramen lacerum is basically formed between:
1. petrous part of the temporal bone
2. Sphenoid bone.
3. Basilar part of the occipital bone
Note: this foramen is covered with fibrous tissue and cartilage during life.
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Posteriorly, between the petrous part of the temporal bone and the occipital bone
is a jugular foramen which is medial to the styloid process and is formed by a
deep notch of the petrous part of the temporal bone and a shallower notch on the
occipital bone. In this foramen the sigmoid sinus becomes the internal jugular
vein, in addition, the glossopharyngeal, vagus and accessory nerves pass through
this foramen (9, 10&11 cranial nerves).
Parts of the occipital bone:
1. Pharyngeal tubercle which is a small prominence on the undersurface of the
basilar part (the most anterior part) of the occipital bone in the midline. This
pharyngeal tubercle gives attachment to the raphe of the pharynx; the pharyngeal raphe is
where the tendons of the constrictor muscles of the pharynx (superior, middle and
inferior) insert.
There are also the two occipital condyles where the tendons of constrictor muscles of the
pharynx (superior, middle, inferior) insert.
2. Occipital condyles articulate with the superior aspect of the lateral masses of the
first cervical vertebra (atlas); the two occipital condyles are on either side of the
foramen magnum.
There is the foramen magnum in the inferior part of the bone; within this foramen the
medulla oblongata connects with the spinal cord and the vertebral arteries, spinal arteries
and accessory (XI) nerve pass.
Superior to the foramen magnum is the external occipital protuberance which is the most
prominent projection of the posterior surface of the bone. The two superior nuchal lines
extend laterally from the protuberance.
3. Hypoglossal canal is superior to the occipital condyle and it is for transmission of
the hypoglossal nerve.
4. External occipital protuberance is posterior to the foramen magnum in the
midline.
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Base of the skull
The calvarium is the skullcap (top of the cranial cavity-roof of the
skull) while the vault of the skull is the inner space of the cranium
occupied by the brain. When you remove the calvaria, you can see
the floor of the cranial cavity which is referred to as the base of the
skull. The base of the skull is basically a depression that is divided
into 3 cranial fossae which lie at three different levels (anterior,
middle and posterior).
The neurocranium is the braincase
of the skull; it is divided into the
base and the calvarium. The
calvarium can be used
alternatively with the vault of the
skull which is the space in the
skull within the neurocranium
occupied by the brain
1. The anterior cranial fossa:
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the highest and most anterior
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The orbital plate of the frontal bone form its floor
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In the midline, there are two structures: the crista gali which is an upward
projection of the ethmoid bone and the cribriform (perforated) plate through
which the fibers of the olfactory never (cranial nerve 1) pass.
2. The middle cranial fossa
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is posterior to the anterior fossa and is separated from it by the lesser wings of
the sphenoid bone
It looks like a butterfly with a
narrow middle portion formed by the
body of the sphenoid bone and two
lateral expansions formed by the
greater wings of the sphenoid bone
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it’s also made up of parts of the
temporal and parietal bones
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In the greater wing there is the optic
canal which transmits the optic
nerve and ophthalmic artery (a
branch of internal carotid artery)
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separating the lesser wing from the
greater is the superior orbital fissure (transmits the superior ophthalmic artery)
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There is the foramen rotundum (transmits the maxillary division of the
trigeminal nerve), posterolateral to it is the foramen ovale (transmits the
mandibular division of the trigeminal nerve-cranial nerve #5) and finally
foramen spinosum (transmits the middle meningeal artery).
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The Superior orbital fissure transmits the superior ophthalmic nerve.
3. The posterior cranial fossa
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which is the most posterior, largest and deepest fossa
It is separated from the middle cranial fossa by the petrous part of the temporal
bone
In this fossa is the internal acoustic (auditory) meatus which transmits the 7th
and 8th cranial nerves
Edited by: Cyrine katanani