THE SKULL
(2)
Face
(Viscerocranium)
• Determine our facial appearance.
• 14 individual bones
• Bones fuse to house the orbits of the eyes, nasal
and oral cavities, as well as the sinuses.
• The facial bones are:
• Zygomatic (2) – Forms the cheek bones of the face.
• Lacrimal (2) – The smallest bones of the face. They
form part of the medial wall of the orbit.
• Nasal (2)
• Inferior nasal conchae (2) – Located within the nasal
cavity.
• Palatine (2) – Situated at the rear of oral cavity, and
forms part of the hard palate.
• Maxilla (2) – Comprises part of the upper jaw and hard
palate.
• Vomer – Forms the posterior aspect of the nasal
septum.
• Mandible (jaw bone)
The maxilla
• Also known as the upper jaw.
This bone consists of five major parts:
• Body of the maxilla
: It contains the maxillary
sinuses and contributes to the floor of the orbit
• Alveolar process
: forms the maxillary dental arch.
• Frontal process
: forms the medial border of the
orbit.
• Zygomatic process
: contributes to the zygomatic
arch together with the zygomatic bone.
• Palatine process
: constitutes the roof of the mouth
and floor of the nasal cavity.
Cranial fossae
• The cranial cavity is divided into three
distinct depressions
The anterior cranial fossa is the most
shallow and superior of the three cranial
fossae.
• Three bones: the frontal bone, ethmoid
bone and sphenoid bone.
• It lies superiorly over the nasal and
orbital cavities. The fossa
accommodates the anteroinferior
portions of the frontal lobes of the
brain.
Contents of anterior cranial fossa
• The crista galli acts as a point of attachment for
the falx cerebri.
• The cribriform plate which supports the olfactory
bulb and has numerous foramina that transmit
vessels and nerves.
• The anterior clinoid processes serve as a place of
attachment for the tentorium cerebelli (a sheet of
dura mater that divides the cerebrum from the
cerebellum).
• The lesser wings of the sphenoid bone also
separate the anterior and middle cranial fossae.
Foramina in the anterior cranial fossa
• The cribriform plate is a sheet of bone seen either side of the crista
galli which contains numerous small foramina – these transmit
olfactory nerve fibres (CN I) into the nasal cavity.
• The cribriform plate also contains two larger foramen:
• Anterior ethmoidal foramen
– transmits the anterior ethmoidal artery, nerve and vein.
• Posterior ethmoidal foramen
– transmits the posterior ethmoidal artery, nerve and vein.
The Middle Cranial Fossa
• Located centrally in the cranial floor.
• Butterfly shaped
• Accommodating the pituitary gland
and two lateral parts accommodating
the temporal lobes of the brain.
• Three bones – the sphenoid bone and
the two temporal bones
Foramina of the middle cranial fossa
Foramina of the Sphenoid Bone
• The
optic canals
: transmit the optic nerves (CN II) and
ophthalmic arteries into the orbital cavities.
Immediately lateral to the central part of the middle cranial
fossa are four foramina:
• The
superior orbital fissure
opens anteriorly into the orbit.
It transmits the oculomotor nerve (CN III), trochlear nerve
(CN IV), ophthalmic branch of the trigeminal nerve (CN
V1), abducens nerve (CN VI), opthalmic veins and
sympathetic fibres.
• The
foramen rotundum
transmits the maxillary branch of
the trigeminal nerve (CN V2).
• The
foramen ovale
transmits the mandibular branch of
the trigeminal nerve (CN V3) and accessory meningeal
artery.
• The
foramen spinosum
transmits the middle meningeal
artery, middle meningeal vein and a meningeal branch of
CN V3.
Foramina of the Temporal Bone
• Carotid canal –
• located posteriorly and medially to the foramen
ovale.
• Transmits the internal carotid artery, internal
carotid venous plexus and sympathetic nerve
plexus from the neck into the cranial cavity.
• At the junction of the sphenoid, temporal
and occipital bones is the foramen lacerum.
Carotid canal
The posterior cranial fossa
• The most posterior and deep of the
three cranial fossae.
• It accommodates the brainstem and
cerebellum.
• Three bones: the occipital bone and the
two temporal bones.
Foramina
Temporal Bone
• The internal acoustic meatus is an oval opening in the posterior
aspect of the petrous part of the temporal bone. It transmits the
facial nerve (CN VII), vestibulocochlear nerve (CN VIII) and
labyrinthine artery.
Occipital Bone
• Foramen magnum
, lies centrally in the floor of the posterior cranial
fossa.
• It is the largest foramen in the skull. It transmits the medulla of the
brain, meninges, vertebral arteries, spinal accessory nerve
(ascending), dural veins and anterior and posterior spinal arteries.
• The
jugular foramina
are situated either side of the foramen
magnum. Each transmits the glossopharyngeal nerve, vagus nerve,
spinal accessory nerve (descending), internal jugular vein, inferior
petrosal sinus, sigmoid sinus and meningeal branches of the
ascending pharyngeal and occipital arteries.
• Hypoglossal canal
: immediately superior to the anterolateral margin
of the foramen magnum . It transmits the hypoglossal nerve
through the occipital bone.
• Posterolaterally to the foramen magnum lies the cerebellar fossae.
These are bilateral depressions that house the cerebellum. They are
divided medially by a ridge of bone, the internal occipital crest.
Jugular bulb
Inferior petrosal and sigmoid sinuses
Labyrinthine artery
Middle meningeal artery
Middle meningeal vein
Foramen spinosum
Meningeal branch of CN V3
Scalp
• Layers of skin and subcutaneous tissue that cover the
bones of cranial vault.
• Skin – contains numerous hair follicles and sebaceous
glands (thus a common site for sebaceous cysts).
• Dense Connective tissue – connects the skin to the
epicranial aponeurosis. It is richly vascularised and
innervated.
• The blood vessels within the layer are highly adherent to the
connective tissue.
• Epicranial Aponeurosis – a thin, tendon-like structure
that connects the occipitalis and frontalis muscles.
• Loose Areolar Connective Tissue – a thin connective
tissue layer.
• It contains numerous blood vessels, including emissary veins
which connect the veins of the scalp to the diploic veins and
intracranial venous sinuses.
• Danger area
• Periosteum – the outer layer of the skull bones.
Scalp
• Arterial Supply
• Branches of external carotid artery and the ophthalmic
artery (a branch of the internal
carotid)
• Venous Drainage
• The superficial drainage follows the arterial supply
• The deep (temporal) region of the skull is drained by
the pterygoid venous plexus. Drain into the maxillary
vein.
• The veins of the scalp
connect to the diploic veins
of the skull via valveless emissary veins
. This
establishes a connection between the scalp and the
dural venous sinuses.
• Innervation
• The scalp receives cutaneous innervation from branches
of the trigeminal nerve or the cervical nerve roots.