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Occipital Bone
The occipital bone
contributes to the posterior, lateral and inferior surfaces of
the cranium. The following features are found on this bone:
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foramen magnum - large circular
opening that connects the cranial and spinal
cavities. |
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occipital condyles - processes that
articulate with the first cervical vertebra. |
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external occipital protuberance - midline
bump on the external surface. |
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jugular notch - together with the
temporal bone forms the jugular foramen. |
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hypoglossal canal - openings
superior to the occipital condyles through which the hypoglossal
nerves pass. |
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Parietal Bones
These bones contribute
to the superior and lateral surface of the cranium. |
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Frontal Bone
The frontal bones have
frontal and orbital parts.
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Frontal (Squamous) Part - the part
of the frontal bone that underlies the forehead.
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frontal (metopic) suture - suture
between the frontal bones that usually disappears
by age 8. |
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supraorbital margin - edge of
the frontal part that forms the superior border of
the orbits. |
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supraorbital foramen or notch
- opening or notch in the middle of the
supraorbital margin. |
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superciliary arches - thickened
ridges over the supraorbital margins that supports
the eyebrows. |
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Orbital Part - the part that forms
the roof of the orbit.
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lacrimal fossa - depression
on the inferior surface of the orbital part that accommodates
the lacrimal gland. |
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Temporal Bones
The temporal bones
contribute to the lateral and inferior walls of the cranium.
The temporal bone can be divided into three parts:
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Squamous part
The
squamous part forms the lateral surface that
borders the squamous suture. Features found here
include: |
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zygomatic process - forms the
inferior margin of the squamous part. This process
with the temporal process of the zygomatic bone
forms the zygomatic arch (cheekbone). |
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mandibular fossa - depression
on the inferior base of the zygomatic process that
articulates with the mandible. |
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articular tubercle - elevation
anterior to the mandibular fossa. |
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Tympanic part
This
part is the region that surrounds the external
acoustic meatus or external auditory canal.
This passageway ends as a tympanic
membrane. |
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Petrous part
This is
the largest most massive part of the temporal bone
that houses the senses of hearing and balance.
Features on this part are:
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mastoid process - bulge
posterior and inferior to the external
acoustic meatus. Contains mastoid
sinuses. |
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styloid process - sharp
process near the mastoid process to which
ligaments and tendons attach. |
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stylomastoid foramen - opening
between the base of the styloid and mastoid
processes through which the facial nerve passes.
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jugular fossa - depression
on the temporal bone that together with the
jugular notch of the occipital bone forms
the jugular foramen. |
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carotid canal - passageway
by which the internal carotid artery penetrates
the skull and reaches the brain. |
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foramen lacerum - jagged
opening between the temporal and
occipital bones. This is not an opening in
the living skull as it is closed by hyaline
cartilage. |
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internal acoustic meatus - canal
on the medial side of the petrous part
through which nerves and vessels supplying
the inner ear and the facial nerve pass. |
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Sphenoid
This complex bone
articulate with every other cranial bone. Although large, most
of the sphenoid is hidden by more superficial bones. The
sphenoid can be divided into the following parts:
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Body
The body
is the central portion of the sphenoid. A
prominent feature of the body is the sella
turcica ("Turkish saddle") that
forms a bony enclosure around the pituitary
gland. The sella turcica can be divided into
the following parts:
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hypophyseal fossa - depression
in which the pituitary gland rests
("seat of saddle"). |
tuberculum sellae - anterior
border of the sella turcica ("horn of
saddle").
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optic groove - groove
directly anterior to the tuberculum
sellae. |
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optic canals - openings
at either end of the optic groove
through which the optic nerves pass. |
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dorsum sellae - posterior
border of the sella turcica ("back of
saddle") |
To the left is a picture
of a Turkish saddle from the Smithsonian
given to Theodore Roosevelt as a gift. |
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Lesser Wings
Wing-like
extensions anterior to the sella turcica. |
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Greater Wings
Large wing-like
processes that extend laterally from the body. The
greater wings act as a brace that strengthens the
sides of the skull.
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superior orbital fissure - irregular
slit-like opening between the lesser and
greater wings. |
The greater wings near their attachment to
the body have the following openings:
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foramen rotundum - a
round opening. |
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foramen ovale - an
oval opening. |
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foramen spinosum - opening
where the greater wings form a sharp
process called the sphenoidal
spine. |
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Pterygoid Processes
Extending
downward on either side of the body are processes
called the pterygoid processes. These processes
form plates that permit muscle attachment. Pterygoid
canals are present at the base of these
processes. |
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Ethmoid
This irregular bone
forms part of the orbital complex, floor of the cranium, roof
of the nasal cavity, and part of the nasal septum. Features of
this bone include:
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cribriform plate - superior surface
of the ethmoid perforated by olfactory foramina through
which the olfactory nerves pass. |
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crista galli - prominent ridge in
the middle of the cribriform plate and an attachment
point for the falx cerebri. |
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lateral masses - entire bony masses
attached on either side of the cribriform plate. The
lateral masses include:
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superior nasal conchae and middle
nasal conchae - scroll-like medial projections
into the nasal cavity. |
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ethmoidal labyrinth - cells
in the interior of the lateral masses that open
into the nasal cavity. |
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perpendicular plate - bony
partition underneath the cribriform plate that forms
part of the nasal septum.
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