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Index | The
Last updated 30 March 2006
The skull, the skeleton of the head,
is the most complex bony structure in the body because it:
- Encloses the brain,
which is irregular in shape;
- Houses the organs of special senses
for seeing, hearing, tasting, and smelling; and
- Surrounds the openings in to the
digestive and respiratory tracts.
- In the anatomical position, the skull is oriented so that
the inferior margin of the orbit (eye socket) and the
superior margin of the external acoustic meatus (auditory
canal) are horizontal. This is called the orbitomenial plane (Frankfort
- The term cranium (L.
skull) is sometimes used when referring to the skull without the mandible
(lower jaw), but the cranium is often used when referring
to the part of the skull containing the brain.
- The superior part is the box-like structure called the calvaria (cranial vault, brain
case); the remainder of the cranium, including the
maxilla (upper jaw), orbits (eyeball sockets) and nasal
cavities, forms the facial skeleton.
- The term skullcap
(calotte) refers to the superior part of the calvaria,
which is removed during autopsies and dissections. The
inferior aspect of the cranium is called the cranial base.
of the Skull
- The skull is comprised of many bones that are closely
fitted together. A series of flat bones are united by
interlocking sutures to form the calvaria, and a group of
irregular bones form the face and the cranial base.
- The skull as a whole is of greater
importance to most health professionals than are its
constituent bones, but it is important to
understand how the skull is constructed.
- Except for the mandible and the auditory ossicles of the
middle ear, rigid sutures join the bones of the adult
skull. The cranium is essentially a
single complex bone.
- Although the adult skull is rigid, the bones forming it
in infants and children grow as individual bones undergo
remodelling. Furthermore, relationships among the various
bones are constantly changing during these developmental
of the Calvaria
Frontal Bone (pp. 644-5)
- The forehead (L. frons) is formed by the smooth,
broad, convex plate of bone called the frontal
- In foetal skulls, the halves of the frontal squama are
divided by a metopic suture
(G. metopon, forehead).
- In most people, the halves of the frontal bone begin to
fuse during infancy and the suture between is usually not
visible after 6 years of age.
- The frontal bone forms the thin roof of the orbits (eye
- Just superior to and parallel with each supraorbital
margin is a bony ridge, the superciliary
arch, which overlies the frontal
sinus. This arch is more pronounced in males.
- Between these arches there is a gently, rounded, medial
elevation called the gabella;
this term derives from the Latin word glabellus
meaning smooth and hairless. In most people, the skin
over the gabella is hairless.
- The slight prominences of the forehead on each side,
superior to the superciliary arches, are called frontal eminences (tubers).
- The supraorbital foramen
(occasionally a notch), which transmits the supraorbital
vessels and nerve is located in the medial part of the
- The frontal bone articulates with the two parietal bones
at the coronal suture.
- It also articulates with the nasal bones at the frontonasal suture. At the
point where this suture crosses the internasal
suture in the medial plane, there is an
anthropological landmark called the nasion
(L. nasus, nose). The depression is located at the
root of the nose, where it joins the cranium.
- The frontal bone also articulates with the zygomatic,
lacrimal, ethmoid, and sphenoid bones.
- In about 8% of adult skulls, a remnant of the inferior
part of the metopic (interfrontal) suture is visible. It
may be mistaken in radiographs for a fracture line by
- The superciliary arches are relatively sharp ridges of
bone and a blow to them may lacerate the skin and cause
- Bruising of the skin over a superciliary arch causes
tissue fluid and blood to accumulate in the surrounding
connective tissue, which gravitates into the upper eyelid
and around the eye. This results in swelling and a
- Compression of the supraorbital
nerve as it emerges from its foramen causes
considerable pain, a fact that may be used by
anaesthesiologists and anaesthetists to determine the
depth of anaesthesia and by physicians attempting to
arouse a moribund (L. dying) patient.
Parietal Bones (p. 645)
- The two parietal bones (L. paries, wall) form
large parts of the walls of the calvaria.
- On the outside of these smooth convex bones, there are
slight elevations near the centre called parietal eminences.
- The middle of the lateral surfaces of the parietal bones
is crossed by two curved lines, the superior and inferior
- The superior temporal line indicates an attachment of the
temporal fascia; the
inferior temporal line marks the superior limit of the temporalis muscle.
- The parietal bones articulate with each other in the
median plane at the sagittal suture.
The medial plane of the body passes through the sagittal
- The inverted V-shaped suture between the parietal bones
and the occipital bones is called the lambdoid
suture because of its resemblance to the
letter lambda in the
- The point where the parietal and occipital bones join is
a useful reference point called the lambda. It can be
felt as a depression in some people.
- In addition to articulation with each other and the
frontal and occipital bones, the parietal bones
articulate with the temporal bones and the greater wings
of the sphenoid bone.
- In foetal and infant skulls, the bones of the calvaria
are separated by dense connective tissue membranes at
- The large fibrous area where several sutures meet are
called fonticuli or fontanelles.
- The softness of these bones and looseness of their
connections at these sutures enable the calvaria to
undergo changes of shape during birth called molding. Within a day or so
after birth, the shape of the infants calvaria
returns to normal.
- The loose construction of the new-born calvaria also
allows the skull to enlarge and undergo remodelling
during infancy and childhood. Relationships between the
various bones are constantly changing during the active
- The increase in the size of the cranium is greatest
during the first 2 years, the period of most rapid
postnatal growth of the brain.
- The cranium normally increases in capacity until about 15
or 16 years of age; thereafter the cranium usually
increases only slightly in size as its bones thicken for
3 to 4 years.
Temporal Bones (p. 645)
- Click here
for a diagram of the temporal bone - lateral aspect.
- Click here
for a diagram of the temporal bone - inferior aspect.
- Click here
for a diagram of the temporal bone - cerebral surface.
- Click here
for a diagram of the temporal bone - cerebellar surface.
- The sides and base of the skull are formed partly by
- Each bone consists of four morphologically distinct parts
that fuse during development (squamous, petromastoid, and
tympanic parts and the styloid process).
- The flat squamous part
is external to the lateral surface of the temporal lobe
of the brain.
- The petromastoid part
encloses the internal ear and mastoid
cells and forms part of the base of the skull.
- The tympanic part
contains the bony passage from the auricle (external
ear), called the external acoustic
meatus. The petromastoid part also forms a
portion of the bony wall of the tympanic cavity (middle
ear). The meatus and tympanic cavity are concerned with
the transmission of sound waves.
- The slender, pointed styloid
process of the temporal bone gives attachment
to certain ligaments and muscles (e.g., the stylohyoid
muscle that elevates the hyoid bone).
- The temporal bone articulates at sutures with the
parietal, occipital, sphenoid, and zygomatic bones.
- The zygomatic process of
the temporal bone unites with the temporal process of the
zygomatic bone to form the zygomatic
arch. The zygomatic arches form the widest
part of the face.
- The head of the mandible
articulates with the mandibular
fossa on the inferior surface of the zygomatic
process of the temporal bone.
- Anterior to the mandibular fossa is the articular tubercle.
- Because the zygomatic arches are the widest parts of the
face and are such prominent facial features, they are
commonly fractured and depressed. A fracture of the
temporal process of the zygomatic bone would likely
involve the lateral wall of the orbit and could injure
Sphenoid Bone (pp. 645, 650)
- Click here for a
diagram of the sphenoid bone - anterior aspect.
- Click here for a
diagram of the sphenoid bone - posterior aspect.
- This is a wedge-shaped bone (G. sphen, wedge) is
located anteriorly to the temporal bones.
- It is a key bone in the cranium
because it articulates with eight bones
(frontal, parietal, temporal, occipital, vomer,
zygomatic, palatine, and ethmoid).
- It main parts are the body
and the greater and lesser wings,
which spread laterally from the body.
- The superior surface of its body is shaped like a Turkish
saddle (L. sella, a saddle); hence its name sella turcica.
- It forms the hypophyseal fossa which contains the
hypophysis cerebri or pituitary
- The sella turcica is bounded posteriorly by the dorsum sellae, a square plate
of bone that projects superiorly and has a posterior clinoid process on
- Inside the body of the sphenoid bone, there are right and
left sphenoid sinuses.
The floor of the sella turcica forms the roof of these
- Studies of the sella turcica and hypophyseal fossa in
radiographs or by other imaging techniques are important
because they may reflect pathological changes such as a pituitary tumour or an
aneurysm of the internal carotid artery. Decalcification
of the dorsum sellae is one of the signs of a generalised
increase in intracranial pressure.
Occipital Bone (p. 650)
- Click here for a
diagram of the external base of the skull.
- This bone forms much of the base and posterior aspect of
- It has a large opening called the foramen
magnum, through which the cranial cavity
communicates with the vertebral canal.
- It is also where the spinal cord becomes continuous with
the medulla (oblongata) of the brain stem.
- The occipital bone is saucer-shaped and can be divided
into four parts: a squamous part
(squama), a basilar part
(basioccipital part), and two lateral
parts (condylar parts).
- These four parts develop separately around the foramen
magnum and unite at about the age of 6 years to form one
- On the inferior surfaces of the lateral parts of the
occipital bone are occipital
condyles, where the skull articulates with C1
vertebra (the atlas) at the atlanto-occipital joints.
- The internal aspect of the squamous part of the occipital
bone is divided into four fossae: the superior two for
the occipital poles of the cerebral hemispheres, and the
inferior two, called cerebellar
fossae, for the cerebellar hemispheres.
of the Face
- Most of the facial skeleton is formed by nine bones: four
paired (nasal, zygomatic, maxilla, and palatine) and one
- The calvaria of the new-born infant is large compared
with the relatively small fascial skeleton.
- This results from the small size of the jaws and the
almost complete absence of the maxillary and other paranasal sinuses in the
- These sinuses form large spaces in the adult facial
skeleton. As the teeth and sinuses develop during infancy
and childhood, the facial bones enlarge.
- The growth of the maxillae between the ages of 6 and 12
years accounts for the vertical elongation of the
Bones (p. 651)
- These bones may be felt easily because they form the bridge of the nose.
- The right and left nasal bones articulate with each other
at the internasal suture.
- They also articulate with the frontal bones, the
maxillae, and the ethmoid bones.
- The mobility of the anteroinferior portion of the nose,
supported only by cartilages, serves as a partial
protection against injure (e.g., a punch in the nose).
However, a hard blow to the anterosuperior bony portion
of the nose may fracture the nasal bones (broken nose).
- Often the bones are displaced sideways and/or
Maxillae (p. 651)
- The skeleton of the face between the mouth and the eyes
is formed by the two maxillae.
- They surround the anterior nasal
apertures and are united in the medial plane
at the intermaxillary suture
to form the maxilla (upper jaw).
- This suture is also visible in the hard
palate, where the palatine processes of the
- Each adult maxilla consists of: a hollow body that contains a large maxillary sinus; a zygomatic process that
articulates with its mate on the other side to form most
of the hard palate; and alveolar
processes that form sockets for the maxillary
- The maxillae also articulate with the vomer, lacrimal,
sphenoid, and palatine bones.
- The body of the maxilla
has a nasal surface that
contributes to the lateral wall of the nasal cavity; an orbital surface that forms
most of the floor of the orbit; an infratemporal
surface that forms the anterior wall of the
infratemporal fossa; and an anterior
surface that faces partly anteriorly and
partly anterolaterally and is covered buy facial muscles.
- The relatively large infraorbital
foramen, which faces inferomedially, is
located about 1 cm inferior to the infraorbital margin;
it transmits the infraorbital nerve
- The incisive fossa is a
shallow concavity overlying the roots of the incisor
teeth, just a shallow concavity overlying the roots of
the incisor teeth, just inferior to the nasal cavity.
This fossa is the injection site for anaesthesia of the
maxillary incisor teeth.
- If infected maxillary teeth are removed, the bone of the
alveolar processes of the maxillae begins to be
reabsorbed. As a result, the maxilla becomes smaller and
the shape of the face changes.
- Owing to absorption of the alveolar processes, there is a
marked reduction in the height of the lower face, which
produces deep creases in the facial skin that pass
posteriorly from the corners of the mouth.
Mandible (pp. 651, 653-4)
- This is a U-shaped bone and forms the skeleton of the
lower jaw and the inferior part of the face. It is the largest and strongest facial bone.
- The mandibular (lower) teeth project superiorly from
their sockets in the alveolar processes.
- The mandible (L. mandere, to masticate) consists
of two parts: a horizontal part called the body, and two vertical oblong
parts, called rami.
- Each ramus ascends
almost vertically from the posterior aspect of the body.
- The superior part of the ramus has two processes: a
posterior condylar process
with a head or condyle
and a neck, and a sharp anterior coronoid
- The condylar process is separated from the coronoid
process by the mandibular notch,
which forms the concave superior border of the mandible.
- Viewed from the superior aspect, the mandible is
horseshoe-shaped, whereas each half is L-shaped when
- The rami and body meet posteriorly at the angle of the mandible.
- Inferior to the second premolar tooth on each side of the
mandible is a mental foramen
(L. mentum, chin) for transmission of the mental
vessels and the mental nerve.
- In the anatomical position, the rami
of the mandible are almost vertical, except in
infants and in edentulous (toothless) adults.
- On the internal aspect of the ramus, there is a large mandibular foramen.
- It is the oblong entrance to the mandibular
canal that transmits the inferior alveolar
vessels and nerve to the roots of the mandibular teeth.
- Branches of these vessels and the mental nerve emerge
from the mandibular canal at the mental
- Running inferiorly and slightly anteriorly on the
internal surface of the mandible from the mandibular
foramen is a small mylohyoid groove
(sulcus), which indicates the course taken by the mylohyoid nerve and vessels.
- These structures arise from the inferior alveolar nerve
and vessels, just before they enter the mandibular
- The internal surface of the mandible is divided into two
areas by the mylohyoid line,
which commences posterior to the third molar tooth. Just
superior to the anterior end of the mylohyoid line are
two small, sharp mental spines
(genial tubercles), which serve as attachments for the
Zygomatic Bones (p. 655)
- The prominences of the cheeks (L. mala), the
anterolateral rims and much of the infraorbital margins
of the orbits, are formed by the zygomatic bones (malar
- They articulate with the frontal, maxilla, sphenoid, and
- The frontal process of the zygomatic bone passes
superiorly, where it forms the lateral border of the
orbit (eye socket) and articulates with the frontal bone
at the lateral edge of the supraorbital margin.
- The zygomatic bones articulate
medially with the greater wings of the sphenoid bone.
The site of their articulation may be observed on the
lateral wall of the orbit.
- On the anterolateral aspect of the zygomatic bone near
the infraorbital margin is a small zygomaticofacial
foramen for the nerve and vessels of the same
- The posterior surface of the zygomatic bone near the base
of its frontal process is pierced by a small zygomaticotemporal foramen for
the nerve of the same name.
- The zygomaticofacial and zygomaticotemporal nerves,
leaving the orbit through the previously named foramina,
enter the zygomatic bone through small zygomaticoorbital
foramina that pierces it orbital surface.
- The temporal process of the zygomatic bone unites with
the zygomatic process of the temporal bone to form the zygomatic arch.
- This arch can be easily palpated on the side of the head,
posterior to the zygomatic
prominence (malar eminence) at the inferior
boundary of the temporal fossa
- The zygomatic arches form one of the useful landmarks for
determining the location of the pterion.
These arches are especially prominent in emaciated
- A horizontal plane passing medially from the zygomatic
arch separates the temporal fossa superiorly from the
infratemporal fossa inferiorly.
- There are several other, very important bones in the
skull, including the palatine bone, ethmoid bone, vomer,
inferior concha and the ossicles of the ear (malleus,
incus and stapes). These, however, are covered to greater
detail where they are relevant in the head (e.g., ethmoid
bone with the orbit and nasal cavity).
Cranial Foramina and
|Anterior Cranial Fossa
|Foramina in cribiform plates of
the ethmoid bone
||Axons of olfactory cells
|Anterior and posterior ethmoidal
||Vessels and nerves with the same
|Middle Cranial Fossa
||Optic nerve and Ophthalmic artery
|Superior orbital fissure
||Ophthalmic vein, Ophthalmic nerve
(CN V1), Oculomotor nerve (CN III),
Trochlear nerve (CN IV), Abducent nerve (CN VI)
and sympathetic fibres.
||Maxillary nerve (CN V2)
||Mandibular nerve (CN V3),
Lesser petrosal nerve
||Middle meningeal artery and vein,
Meningeal branch of mandibular nerve
|Foramen lacerum - Click here
for a schematic.
||internal carotid artery
|Hiatus of greater petrosal nerve
||Greater petrosal nerve
|Posterior Cranial Fossa
||Medulla and meninges, vertebral
arteries, Spinal root of accessory nerve (CN XI)
||Glossopharyngeal nerve (CN IX),
Vagus nerve (CN X), Accessory nerve (CN XI),
Superior bulb of internal jugular vein, Inferior
petrosal and sigmoid sinuses
||Hypoglossal nerve (CN XII)