SKULL BONES
NEUROCRANIM & VISCEROCRANIUM
5. 10. 2012
Kaan Yücel
M.D., Ph.D.
http://yeditepeanatomy1.org
Dr.Kaan Yücel
http://yeditepeanatomy1.org
Skull bones
The skeleton of the head is the skull. We rather use the ancient Greek term “cranium”, e.g. the cranial nerves.
The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the
bones of the skull are attached to each other by sutures, are immobile, and form the cranium.
The part that is covering the cranial cavity and the brain in it is called neurocranium. The skeleton of the face
is called viscerocranium or facial skeleton. It is the lower part of the cranium.
Out of the 22 bones in the skull, 8 of them are in the neurocranium. They are:
•
1 Frontal bone; the bone in the front of the head
•
1 Occipital bone; the bone at the back of the head
•
2 Parietal bones; “paries” means wall, and these though bones are on the lateral sides of the skull.
•
2 Temporal bones; “temple” has two meanings “time” and “temple”. Time can make more sense for
the temporal bones, as where they are the hair becomes grey first.
•
1 Sphenoid bone in the middle (Greek sphēnoeidēs wedge-shaped)
•
1 Ethmoid bone again in the middle (In Moore’s textbook it is part of the facial skeleton,though)
The skeleton of your face is made up by the remaining 14 bones of the cranium.
They are:
•
Two Nasal bones
•
Two Maxillæ
•
Mandible
•
Two Lacrimal bones
•
Two Zygomatic bones
•
Two Palatines
•
Two Inferior Nasal Conchæ
•
Vomer
The inferior and anterior parts of the frontal lobes of the brain occupy the anterior cranial fossa, the shallowest
of the three cranial fossae. The fossa is formed by the frontal bone anteriorly, the ethmoid bone in the middle, and
the body and lesser wings of the sphenoid posteriorly. The butterfly-shaped middle cranial fossa has a central part
composed of the sella turcica on the body of the sphenoid and large, depressed lateral parts on each side. The bones
forming the lateral parts of the fossa are the greater wings of the sphenoid and squamous parts of the temporal bones
laterally and the petrous parts of the temporal bones posteriorly. The posterior cranial fossa, the largest and deepest
of the three cranial fossae is formed mostly by the occipital bone, but the dorsum sellae of the sphenoid marks its
anterior boundary centrally and the petrous and mastoid parts of the temporal bones contribute its anterolateral
“walls.”
Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of
fibrous tissue; it is met with only in the skull. The major suturae in the skull are; coronal, lambdoid, and sagittal
suturues.
Important landmarks in the skull are:
Bregma: The midline point where the coronal and sagittal sutures intersect
Lambda: The midline point where the sagittal and lambdoid sutures intersect.
Glabella: The most forward projecting point in the midline of the forehead at the level of the supra-orbital
ridges and above the nasofrontal suture
Pterion: The point of intersection between the frontal, sphenoid, parietal and the temporal bones
Nasion: The point of intersection between the frontonasal suture and the midsagittal plane.
Gnathion: The most anterior and lowest median point on the border of the mandible
The bones of the calvaria of a newborn infant are separated by membranous intervals. They include the
anterior and posterior fontanelles and the paired sphenoidal and mastoid fontanelles.
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1. SKULL
The skeleton of the head is the skull. We rather use the ancient Greek term “cranium”, e.g. the
cranial nerves. The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which
forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile, and form
the cranium. Suture is also a term used in surgical practices as “surgical stitching of a wound”. Actually
suture in anatomy is a type of articulation where two articulation surfaces come together along a line, just
like you sew them with a needle.
We can divide the cranium into two or three parts. Generally into two!
Let’s see, there is one part enclosing the brain; protecting the brain, and there is another part which
makes the skeleton of your face. The part that is covering the cranial cavity and the brain in it is called
neurocranium. The skeleton of the face is called viscerocranium or facial skeleton. It is the lower part of
the cranium. Here the viscera means organ, and on your face there is a list of organs; your mouth, your
nose, your eyes. The prefix neuro in the term neurocranium just refers to the “nerve” telling you that this
part of the skeleton of the head covers the brain and meninges (the membrane covering the brain) within
the cranial cavity.
A third part of the skeleton of the head? The part that covers the upper part of the head; calvaria
(skullcap) “kafatası” in Turkish might be considered as a third part. If you add it into the neurocranium,
then the cranium has two parts. Ok? So the neurocranium has one roof (calvaria) and one floor; the base
(base of the skull) basicranium.
Question: which bones make up the neurocranium? Out of the 22 bones of the cranium, 8 of them
belong to the neurocranium. Some of them are paired which means you can find one on the right side, and
one on the left side, and some of them are single.
 1 Frontal bone; the bone in the front of the head
 1 Occipital bone; the bone at the back of the head
 2 Parietal bones; “paries” means wall, and these though bones are on the lateral sides of the skull.
 2 Temporal bones; “temple” has two meanings “time” and “temple”. Time can make more sense for the
temporal bones, as where they are the hair becomes grey first.
 1 Sphenoid bone in the middle (Greek sphēnoeidēs wedge-shaped)
 1 Ethmoid bone again in the middle (In Moore’s textbook it is part of the facial skeleton,though)
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As you see only the temporal bones and the parietal bones above them are paried (bilateral), and
the other four bones are single (unilateral) which make the eight bones of the neurocranium.
The neurocranium has a dome-like roof, the calvaria (skullcap), and a floor or cranial base (basicranium).
The bones making the calvaria are primarily flat bones (frontal, parietal, and occipital). The bones
contributing to the cranial base are primarily irregular bones with substantial flat portions (sphenoidal and
temporal). The ethmoid bone is an irregular bone that makes a relatively minor midline contribution to the
neurocranium but is also part of the viscerocranium. Watch out! Although there is only a minor
contribution of the ethmoid bone to the neurocranium, it is counted under the bones of the neurocranium.
The skeleton of your face is made up by the remaining 14 bones of the cranium.
They are:

Two Nasal bones

Two Maxillæ

Mandible

Two Lacrimal bones

Two Zygomatic bones

Two Palatines

Two Inferior Nasal Conchæ

Vomer
The viscerocranium forms the anterior part of the cranium and consists of the bones surrounding the
mouth (upper and lower jaws), nose/nasal cavity, and most of the orbits (eye sockets or orbital cavities).
The viscerocranium consists of 14 irregular bones: 2 singular bones centered on or lying in the midline
(mandible and vomer) and 6 bones occurring as bilateral pairs (maxillae; inferior nasal conchae; and
zygomatic, palatine, nasal, and lacrimal bones).
The maxillae and mandible house the teeth—that is, they provide the sockets and supporting bone for the
maxillary and mandibular teeth. The maxillae contribute the greatest part of the upper facial skeleton,
forming the skeleton of the upper jaw, which is fixed to the cranial base. The mandible forms the skeleton
of the lower jaw, which is movable because it articulates with the cranial base at the temporomandibular
joints.
Several bones of the cranium (frontal, temporal, sphenoid, and ethmoid bones) are pneumatized
bones, which contain air spaces (air cells or large sinuses), presumably to decrease their weight. The total
volume of the air spaces in these bones increases with age.
What we have to do now is to see what each bone has: bone markings & formations. The
information on each bone can be presented in two ways. The textbooks (Moore’s, Gray’s, and Snell’s)
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present the information on cranial bones by talking about the views from anterior, inferior and lateral
aspects. Another way might be talking about each bone one by one.I will do it that way. On the other hand,
I will also give you the perspective of “what you see when you look at the anterior part of the skull or from
an inferior view” at the end. Remember! To remember “repeating” is the best way! So you will have both
the regional (bones one by one) perspective and also the views perspective (that of the textbooks).
Figure 1. Skull bones (lateral view)
http://images.tutorvista.com/content/locomotion-animals/human-skull-structure.jpeg
2. BONES OF THE NEUROCRANIUM
2.1. FRONTAL BONE (OS FRONTALE)
Figure 2. Frontal bone
http://www.bleaching-dental.com/img/news/126.jpg
The biggest part of the brain (one third of a brain
hemisphere); the frontal lobe mostly resides on the frontal lobe.
The frontal bone forms the forehead. It also contributes to the
formation of two cavities; the orbital cavity where the eyes are
located and the nasal cavity (the cavity inside your nose).
The frontal bone consists of two portions:
squama (etymology: Latin, squama: scale; squama frontalis)- vertical portion
corresponding with the region of the forehead
orbital portion (frontal orbit; orbita frontalis)– horizontal partion
enters into the formation of the roofs of the orbital and nasal cavities
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Figure 3. Frontal bone, squamous part
http://virtual.yosemite.cc.ca.us/rdroual/Lecture%20Notes/Unit%202/chapter_6_axial_skeleton_copy%20with%20figures.htm
So you should take the frontal bone as two pieces; one flat surface (squama) and one horizontal
surface forming the roof of the orbit (the nest for the eye). From now on, if a cranial bone has a flat,
smooth surface, it will be named as squamous part (just like the one in the occipital bone, back of the
head).
Anterior view
The supra-orbital margin of the frontal bone, the angular boundary between the squamous and
the orbital parts, has a supra-orbital foramen or notch in some crania for passage of the supra-orbital
nerve and vessels. Just superior to the supra-orbital margin and the rim of the orbit there is a ridge, the
superciliary arch. The prominence of these ridges, deep to the eyebrows, is generally greater in males.
Between the superciliary arches is a small depression (glabella). The superciliary arches extend laterally on
each side from the glabella. In some people, frontal eminences are also visible, giving the calvaria an
almost square appearance.
Medially, the frontal bone projects inferiorly forming a part of the medial rim of the orbit. Laterally,
the zygomatic process of the frontal bone projects inferiorly forming the upper lateral rim of the orbit.
This process articulates with the frontal process of the zygomatic bone.
In some adults a metopic suture, a persistent frontal suture or remnant of it, is visible in the midline
of the glabella, the smooth, slightly depressed area between the superciliary arches. The estimated
prevalence is 1 in 15,000 live births with a 3:1 male:female ratio.
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Figure 4. Frontal bone (anterior view)
http://www.csuchico.edu/anth/Module/frontal.html
The internal surface of the squama frontalis of the frontal bone is concave and presents in
the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to
form a ridge, the frontal crest. The frontal crest is a median bony extension of the frontal bone. At its base
is the foramen cecum (blind hole) of the frontal bone, which gives passage to vessels during fetal
development. Nasal process is the downward projection of the nasal part of the frontal bone which
terminates as the nasal spine.
Figure 5. Frontal bone (inner surface)
http://www.bartleby.com/107/illus135.html
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2.2. PARIETAL BONES
The two parietal bones unite and form the sides and roof of the cranium. Each bone is irregularly
quadrilateral in form. The external surface is convex, smooth, and marked near the center by an eminence,
the parietal eminence (tuber parietale). Crossing the middle of the bone in an arched direction are two
curved lines, the superior and inferior temporal lines. The parietal foramen is a small, inconstant aperture
located posteriorly in the parietal bone near the sagittal suture. Paired parietal foramina may be present.
Figure 6. Parietal bone (lateral view)
http://medical-dictionary.thefreedictionary.com/parietal+bone
Figure 7. Parietal bones (anterior view)
http://aftabphysio.blogspot.com/2010/09/bones-of-skull.html
2.3. TEMPORAL BONES
The temporal bones are situated at the sides and base of the skull. The temporal bone has the
temporal lobe on which is important for a long list of functions including memory, emotional memory,
hearing. It has the canal that goes to the ear.
The temporal bone contributes most of the lower portion of the lateral wall of the cranium.
Each temporal bone has five parts:
1) Squamous part
2) Tympanic part
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3) Mastoid part
4) Petrous part
5) Styloid process
The squamous part has the appearance of a large flat plate, forms the anterior and superior parts of
the temporal bone, contributes to the lateral wall of the cranium, and articulates anteriorly with the
greater wing of the sphenoid bone at the sphenosquamous suture, and with the parietal bone superiorly
at the squamous suture. The zygomatic process is an anterior bony projection from the lower surface of
the squamous part of the temporal bone that initially projects laterally and then curves anteriorly to
articulate with the temporal process of the zygomatic bone to form the zygomatic arch.
The squamous part lies just lateral to the greater wing of the sphenoid. It participates in the
temporomandibular joint. It contains the mandibular fossa, which is a concavity where the head of the
mandible articulates with the base of the skull. An important feature of this articulation is the prominent
articular tubercle, which is the downward projection of the anterior border of the mandibular fossa.
The tympanic part of the temporal bone is immediately below the origin of the zygomatic process
from the squamous part of the temporal bone. The external acoustic opening (pore) is the entrance to the
external acoustic meatus (canal), which leads to the tympanic membrane (eardrum). The external acoustic
opening is clearly visible on the surface of this part.
The mastoid part is the most posterior part of the temporal bone. It is continuous with the
squamous part of the temporal bone anteriorly, and articulates with the parietal bone superiorly, and with
the occipital bone posteriorly.
On the lateral edge of the mastoid part lies the cone-shaped mastoid process projecting from its
inferior surface. The mastoid process is a prominent structure and is the point of attachment for several
muscles. On the medial aspect of the mastoid process is the deep mastoid notch, which is also an
attachment point for a muscle.
Immediately lateral to the basilar part of the occipital bone is the petrous part of the temporal
bone. Wedge-shaped in its appearance the petrous part of the temporal bone is between the greater
wing of the sphenoid anteriorly and the basilar part of the occipital bone posteriorly. The apex forms one
of the boundaries of the foramen lacerum, an irregular opening filled in life with cartilage. Posterolateral
from the foramen lacerum along the petrous part of the temporal bone is the large circular opening for the
carotid canal.
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The large opening between the occipital bone and the petrous part of the temporal bone is the
jugular foramen.This foramen is very important as major structures pass through this foramen. The vein
draining the brain exits the skull through the jugular foramen. Later on, in the second year you will learn
the 12 cranial nerves. Three of them pass through the jugular foramen and go to their destinations exiting
the cranium. Anterosuperior to the jugular foramen is the internal acoustic meatus for the passage of two
other cranial nerves. One of them is the nerve for the muscles of the face, and the other is good for the
hearing and balance.
The styloid process is needle-shaped bone marking. It projects from the lower border of the
temporal bone anteromedial to the mastoid process. The styloid process is a point of attachment for
numerous muscles and ligaments. The stylomastoid foramen, transmitting the nerve for the muscles of
the face lies posterior to the base of the styloid process; between the styloid process and the mastoid
process.
Figure 8. Temporal bone
http://medicinembbs.blogspot.com/2011/02/skull-anatomy.html
2.4. SPHENOID BONE
The sphenoid bone is situated at the base of the skull in front of the temporal bones and basilar
part of the occipital bone. It somewhat resembles a bat with its wings extended, and is divided into a
median portion; body, two great and two small wings extending outward from the sides of the body, and
two pterygoid processes which project from it below.
The greater and lesser wings of the sphenoid spread laterally from the lateral aspects of the body
of the bone. The pterygoid processes, consisting of lateral and medial pterygoid plates, extend inferiorly
on each side of the sphenoid from the junction of the body and greater wings. Pterygoid fossa is between
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the two plates. Each medial plate of the pterygoid process ends inferiorly with a hook-like projection, the
pterygoid hamulus.
The sphenoidal crests are formed mostly by the sharp posterior borders of the lesser wings of the
sphenoid bones. The sphenoidal crests end medially in two sharp bony projections, the anterior clinoid
processes.
The sella turcica (L. Turkish saddle) is the saddle-like bony formation on the upper surface of the
body of the sphenoid, which is surrounded by the anterior and posterior clinoid processes. Clinoid means
“bedpost,” and the four processes (two anterior and two posterior) surround the hypophysial fossa, the
“bed” of the pituitary gland, like the posts of a four-poster bed.
The sella turcica is composed of three parts:
1) The tuberculum sellae (horn of saddle): a variable slight to prominent median elevation forming the
posterior boundary of the prechiasmatic sulcus and the anterior boundary of the hypophysial fossa. It lies
behind the chiasmatic groove. On both ends of the tuberculum sellae are middle clinoid processes.
2) The hypophysial fossa (pituitary fossa): a median depression (seat of saddle) in the body of the
sphenoid that accommodates the pituitary gland (L. hypophysis).
3) The dorsum sellae (back of saddle): a square plate of bone projecting superiorly from the body of the
sphenoid. It forms the posterior boundary of the sella turcica, and its prominent superolateral angles make
up the posterior clinoid processes.
On each side of the body of the sphenoid, four foramina perforate the roots of the cerebral surfaces of the
greater wings of the sphenoids:
Superior orbital fissure: Located between the greater and the lesser wings, it opens anteriorly into the
orbit.
Foramen rotundum (round foramen): Located posterior to the medial end of the superior orbital
fissure.
Foramen ovale (oval foramen): A large foramen posterolateral to the foramen rotundum.
Foramen spinosum (spinous foramen): Located posterolateral to the foramen ovale.
The foramen lacerum (lacerated or torn foramen) is not part of the crescent of foramina. This
ragged foramen lies posterolateral to the hypophysial fossa and is an artifact of a dried cranium. In life, it is
partly closed by a cartilage plate.
Figure 9. Sphenoid bone (anterior view)
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Figure 10. Foramina in the sphenoid bone (superior view) and other openings
http://medchrome.com/wp-content/uploads/2011/05/skull-superior.jpg
2.5. OCCIPITAL BONE
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The occipital bone is situated at the back and lower part of the cranium. It is trapezoid in shape and
curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial
cavity communicates with the vertebral canal.
The foramen magnum is the most prominent feature of the cranial base. The major structures
passing through this large foramen:

spinal cord (where it becomes continuous with the medulla oblongata of the brain)

meninges (coverings) of the brain and spinal cord

vertebral arteries

anterior and posterior spinal arteries

spinal accessory nerve (CN XI).
The four parts of the occipital bone are arranged around the foramen magnum:
1) The curved, expanded plate behind the foramen magnum is named the squama.
2) The thick, quadrilateral piece in front of the foramen is called the basilar part.
3) On either side of the foramen is the lateral portion of the occipital bone.
The cranial base is formed posteriorly by the occipital bone, which articulates with the sphenoid bone
anteriorly.
The external occipital protuberance, is usually easily palpable in the median plane; however,
occasionally (especially in females) it may not be prominent. The external occipital crest descends from
the protuberance toward the foramen magnum.
The superior nuchal line marks the superior limit of the neck. It extends laterally from each side of
the protuberance. The inferior nuchal line is less distinct.
On the lateral parts of the occipital bone are two large protuberances, the occipital condyles. The
cranium articulates with the vertebral column by the occipital condyles.
The clivus is a shallow depression, incline (Latin for "slope") behind the dorsum sellæ that slopes
obliquely backward. Posterior to foramen magnum, the posterior cranial fossa is partly divided by the
internal occipital crest into bilateral large concave impressions, the cerebellar fossae. The internal
occipital crest ends in the internal occipital protuberance. Actually, the internal occipital crest is the lower
division of a cross called as cruciate eminence. The cruciate eminence divides the interior surface of the
occipital bone into four fossae. The superior two fossae are triangular and lodge the occipital lobes of the
cerebrum (cerebral fossae). The inferior two are quadrilateral and accommodate the hemispheres of the
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cerebellum (cerebellar fossae). The internal occipital protuberance is the prominent elevation in the
centre of the cruciate eminence.
The hypoglossal canal for the hypoglossal nerve (CN XII) is superior to the anterolateral margin of
the foramen magnum.
Figure 11. Occipital bone (inner surface)
2.6. ETHMOID BONE
Gk, ethmos, sieve sifter, eidos, form
The etmoid bone is exceedingly light and spongy, and cubical in shape; it is situated at the anterior
part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of
these cavities. It consists of four parts: a horizontal or cribriform plate, forming part of the base of the
cranium; a perpendicular plate, constituting part of the nasal septum; and two lateral ethmoidal
labyrinths. The crista galli (L. crest of the cock) is a thick, median ridge of bone posterior to the foramen
cecum (frontal bone), which projects superiorly from the ethmoid. On each side of the ridge called crista
galli, located in the frontal bone, is the sieve-like cribriform plate of the ethmoid. Its numerous tiny
foramina transmit the olfactory nerves (CN I) from the olfactory areas of the nasal cavities to the olfactory
bulbs of the brain, which lie on this plate.
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Figure 12. Ethmoid Bone
http://medical-dictionary.thefreedictionary.com/ethmoid+bone
Figure 13. Ethmoid bone’s location in the skull
http://www.daviddarling.info/images/ethmoid_bone.jpg
3. CRANIAL FOSSAE
3.1. ANTERIOR CRANIAL FOSSA
The inferior and anterior parts of the frontal lobes of the brain occupy the anterior cranial fossa, the
shallowest of the three cranial fossae. The fossa is formed by the frontal bone anteriorly, the ethmoid bone
in the middle, and the body and lesser wings of the sphenoid posteriorly. The greater part of the fossa is
formed by the orbital parts of the frontal bone, which support the frontal lobes of the brain and form the
roofs of the orbits. This surface shows sinuous impressions (brain markings) of the orbital gyri (ridges) of
the frontal lobes.
3.2. MIDDLE CRANIAL FOSSA
The butterfly-shaped middle cranial fossa has a central part composed of the sella turcica on the
body of the sphenoid and large, depressed lateral parts on each side. The middle cranial fossa is
posteroinferior to the anterior cranial fossa, separated from it by the sharp sphenoidal crests laterally. The
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bones forming the lateral parts of the fossa are the greater wings of the sphenoid and squamous parts of
the temporal bones laterally and the petrous parts of the temporal bones posteriorly. 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.
3.3. POSTERIOR CRANIAL FOSSA
The posterior cranial fossa, the largest and deepest of the three cranial fossae, lodges the
cerebellum, pons, and medulla oblongata. The posterior cranial fossa is formed mostly by the occipital
bone, but the dorsum sellae of the sphenoid marks its anterior boundary centrally and the petrous and
mastoid parts of the temporal bones contribute its anterolateral “walls.” Posterior to foramen magnum,
the posterior cranial fossa is partly divided by the internal occipital crest into bilateral large concave
impressions, the cerebellar fossae.
Figure 14. Cranial fossae
http://tmjc.com.ne.kr/tmj/info/drinfo/images/tm6-6.jpg
4. BONES OF THE VISCEROCRANIUM
4.1. NASAL BONES
The nasal bones are two small oblong bones, varying in size and form in different individuals; they
are placed side by side at the middle and upper part of the face, and form, by their junction, “the bridge”
of the nose. Each has two surfaces and four borders.
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Figure 15. Nasal bone and other facial bones
http://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Illu_facial_bones.jpg/250px-Illu_facial_bones.jpg
4.2. MAXILLÆ (UPPER JAW)
The maxillae are the largest bones of the face, excepting the mandible, and form, by their union,
the whole of the upper jaw. Each assists in forming the boundaries of three cavities: the roof of the mouth,
the floor and lateral wall of the nose and the floor of the orbit. It has two fissures, the inferior orbital and
pterygomaxillary fissures.
Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and palatine. The
maxillae form the upper jaw; their alveolar processes include the tooth sockets (alveoli) and constitute the
supporting bone for the maxillary teeth. The two maxillae are united at the intermaxillary suture in the
median plane. The maxillae surround most of the piriform aperture and form the infra-orbital margins
medially. They have a broad connection with the zygomatic bones laterally and an infraorbital foramen
inferior to each orbit for passage of the infra-orbital nerve and vessels.
Figure 16. Maxilla
http://www.probertencyclopaedia.com/E_MAXILLA.HTM
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4.3. MANDIBLE (LOWER JAW)
The mandible is the largest and strongest bone of the face, serves for the reception of the lower
teeth. It is a U-shaped bone with an alveolar process that supports the mandibular teeth. Dentoalveolar
syndesmosis (gomphosis or socket) is a fibrous joint in which a peglike process fits into a socket
articulation between the root of the tooth and the alveolar process of the jaw (mandile or maxilla).
The mandible consists of a head, a curved, horizontal portion, the body, and two perpendicular
portions, the rami (sing. ramus, which means branch). The two rami of the mandible unite with the ends
of the body nearly at right angles. Just below the head of the mandible, is the neck of the mandible.
The body of mandible is arbitrarily divided into two parts: the lower part is the base of mandible;
the upper part is the alveolar part of mandible. On the superior part of the ramus a condylar and coronoid
process extend upward. The condylar process is involved in articulation of the mandible with the temporal
bone, and the coronoid process is the point of attachment for the temporalis muscle. The head of the
mandible enters the fossa mandibularis in the temporal bone when it comes to the temporomandibular
joint.
Mandibular notch is a deep concavity between the condylar and coronoid processes.
Inferior to the second premolar teeth are the mental foramina for the mental nerves and vessels.
Continuing past this foramen is a ridge (oblique line) passing from the front of the ramus onto the body of
mandible. The oblique line is a point of attachment for muscles that depress the lower lip.
The incisive canal is a continuation forward of the mandibular canal beyond the mental foramen and
below the incisor teeth.
The mental protuberance, forming the prominence of the chin, is a triangular bony elevation inferior to
the mandibular symphysis (L. symphysis menti), the osseous union where the halves of the infantile
mandible fuse. Just lateral to the mental protuberance, on either side, are slightly more pronounced
bumps (mental tubercles).
Interior view
Medial to the condylar process is the pterygoid fossa. Mandibular foramen lies inferior to this fossa.
Lingula is a tongue-like bony process over the mandibular foramen. The internal surface of the body bears
an oblique ridge, the mylohyoid line, which begins a short distance below the last molar tooth as a
prominent crest. Below the mylohyoid line is a concave area, termed the submandibular fossa, which
lodges the submandibular salivary gland. Running forward from the ramus into the submandibular fossa is
the shallow mylohyoid groove which fades out anteriorly. Immediately above the line is the shallow
sublingual fossa for the salivary gland of the same name. The inferior border of the body is marked, a little
to each side of the midline, by the small, roughened digastric fossa for attachment of the anterior belly of
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the digastric muscle. The digastric fossa is on either on either side of the symphysis menti.
Figure 23. Mandible (Lat., mandibula)
http://facialfractures.blogspot.com
4.4. LACRIMAL BONE
The lacrimale bone is the smallest and most fragile bone of the face is situated at the front part of the
medial wall of the orbit.
Figure 17. Lacrimal bone
http://www.upstate.edu/cdb/education/grossanat/hnskullantlb.shtml
4.5. ZYGOMATIC BONES
cheek bones, malar bones
The zygomatic bones are quadrilateral bones. The zygomatic bones form the prominence of the
cheeks, and that is why we also call them as “the cheek bones”. They are located on the maxillae on each
side and inferolateral sides of the orbits. The walls, floor and much of the infra-orbital margins of the orbits
are formed by the zygomatic bones.
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A small zygomaticofacial foramen pierces the lateral aspect of each bone. The zygomatic bones
articulate with the frontal, sphenoid, and temporal bones and the maxillae.
Figure 18. Zygomatic bone’s location in the skull
http://medical-dictionary.thefreedictionary.com/zygomatic+bone
Figure 19. Zygomatic bone
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4.6. PALATINE BONE
The palatine bone is situated at the back part of the nasal cavity between the maxilla and the
pterygoid process of the sphenoid. It contributes to the walls of three cavities: the floor and lateral wall of
the nasal cavity, the roof of the mouth, and the floor of the orbit. It has one horizontal plate, and a vertical
(perpendicular) plate. It also three prolongations; orbital, maxillary (pyramidal) and sphenoidal
processes.
The hard palate (bony palate) is formed by the palatine processes of the maxillae anteriorly and the
horizontal plates of the palatine bones posteriorly. The free posterior border of the hard palate projects
posteriorly in the median plane as the posterior nasal spine. Posterior to the central incisor teeth is the
incisive foramen, in the midline of the bony palate where blood vessels and nerves pass.
Superior to the posterior edge of the palate are two large openings: the choanae (posterior nasal
apertures), which are separated from each other by the vomer (L. plowshare), a flat unpaired bone of
trapezoidal shape that forms a major part of the bony nasal septum.
Figure 20. Palatine bone
http://medical-dictionary.thefreedictionary.com/os+palatinum
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Figure 21. Hard palate
http://www.gla.ac.uk/ibls/US/cal/anatomy/cleftpalate/final/hardp975.htm
4.7. INFERIOR NASAL CONCHA
Concha Nasalis Inferior; Inferior Turbinated Bone
The inferior nasal concha extends horizontally along the lateral wall of the nasal cavity. The anterior
and middle nasal conchae are not separate bones but parts of the ethmoid bone.
Figure 22. Inferior nasal concha
http://www.bcnlp.ac.th/Anatomy/page/apichat/bone/page/inferior-concha.html
4.8. VOMER
Vomer is a small bone in the midline, resting on the sphenoid bone. It contributes to the formation
of the bony nasal septum separating the two choanae.
Figure 24. Vomer
http://www.ask.com/wiki/Vomer
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5. SUTURA
Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of
fibrous tissue; it is met with only in the skull.
5.1. CORONAL SUTURE
Parietal bones articulate with the frontal bone in their front, forming the coronal suture.
5.2. LAMBDOID SUTURE
Parietal bones articulate with the occipital in their behind, forming the lambdoid suture.
5.3 .SAGITTAL SUTURE
Parietal bone articulates with its the opposite side, forming the sagittal suture. Vertex, the most superior
point of the calvaria, is near the midpoint of the sagittal suture.
The coronal suture separates the frontal and parietal bones, the sagittal suture separates the parietal
bones, and the lambdoid suture separates the parietal and temporal bones from the occipital bone.
Figure 26. Suturae
http://upload.wikimedia.org/wikipedia/commons/thumb/0/0d/Human_skull_side_suturas.svg/524px-Human_skull_side_suturas.svg.png
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6. IMPORTANT LANDMARKS
Bregma: The midline point where the coronal and sagittal sutures intersect
Lambda: The midline point where the sagittal and lambdoid sutures intersect.
Glabella: The most forward projecting point in the midline of the forehead at the level of the supraorbital ridges and above the nasofrontal suture
Pterion: The point of intersection between the frontal, sphenoid, parietal and the temporal bones
Nasion: The point of intersection between the frontonasal suture and the midsagittal plane.
Gnathion: The most anterior and lowest median point on the border of the mandible.
Figure 27. Landmarks of the skull
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7. FONTANELLES
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The bones of the calvaria of a newborn infant are separated by membranous intervals. They include
the anterior and posterior fontanelles and the paired sphenoidal and mastoid fontanelles. Palpation of the
fontanelles during infancy, especially the anterior and posterior ones, enables physicians to determine the:
•
Progress of growth of the frontal and parietal bones.
•
Degree of hydration of an infant (a depressed fontanelle indicates dehydration).
•
Level of intracranial pressure (a bulging fontanelle indicates increased pressure on the brain).
The anterior fontanelle, the largest one, is diamond or star shaped; it is bounded by the halves of the
frontal bone anteriorly and the parietal bones posteriorly. Thus it is located at the junction of the sagittal,
coronal, and frontal sutures, the future site of bregma. By 18 months of age, the surrounding bones have
fused and the anterior fontanelle is no longer clinically palpable.
The posterior fontanelle is triangular and bounded by the parietal bones anteriorly and the occipital bone
posteriorly. It is located at the junction of the lambdoid and sagittal sutures, the future site of lambda. The
posterior fontanelle 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.
The sphenoidal and mastoid fontanelles fuse during infancy and are less important clinically than the
midline fontanelles.
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.
Figure 28. Fontanelles
http://medical-dictionary.thefreedictionary.com/fontanelle
CLINICAL ANATOMY
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HEAD INJURIES
Head injuries are a major cause of death and disability. The complications of head injuries include
hemorrhage, infection, and injury to the brain and cranial nerves.
FRACTURES OF THE CRANIAL FOSSAE
In fractures of the anterior cranial fossa, the cribriform plate of the ethmoid bone may be damaged.
Fractures of the middle cranial fossa are common, because this is the weakest part of the base of the skull.
Anatomically, this weakness is caused by the presence of numerous foramina and canals in this region; the
cavities of the middle ear and the sphenoidal air sinuses are particularly vulnerable.
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How the bones are located in the skull?
Which bones/anatomical features do you see in each view
(anterior, lateral, posterior,superior views)?
Anterior view of the skull (Facial- frontal aspect of the cranium)
Figure 29. Anterior view of the skull
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The anterior view of the skull includes the forehead superiorly, and, inferiorly, the orbits, the nasal region, the
part of the face between the orbit and the upper jaw, the upper jaw, and the lower jaw. Features of the anterior or facial
(frontal) aspect of the cranium are the frontal and zygomatic bones, orbits, nasal region, maxillae, and mandible.
The frontal bone, specifically its squamous (flat) part, forms the skeleton of the forehead,
articulating inferiorly with the nasal and zygomatic bones.
The zygomatic bones (cheek bones, malar bones), forming the prominences of the cheeks,
lie on the inferolateral sides of the orbits and rest on the maxillae. The anterolateral rims, walls,
floor, and much of the infra-orbital margins of the orbits are formed by these quadrilateral bones.
The zygomatic bones articulate with the frontal, sphenoid, and temporal bones and the maxillae.
Inferior to the nasal bones is the pear-shaped piriform aperture, the anterior nasal opening
in the cranium. The bony nasal septum can be observed through this aperture, dividing the nasal
cavity into right and left parts. On the lateral wall of each nasal cavity are curved bony plates, the
nasal conchae.
The maxillae form the upper jaw; their alveolar processes include the tooth sockets (alveoli)
and constitute the supporting bone for the maxillary teeth. The two maxillae are united at the
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intermaxillary suture in the median plane. The maxillae surround most of the piriform aperture and
form the infra-orbital margins medially. They have a broad connection with the zygomatic bones
laterally and an infraorbital foramen inferior to each orbit for passage of the infra-orbital nerve and
vessels.
The mandible is a U-shaped bone with an alveolar process that supports the mandibular
teeth. It consists of a horizontal part, the body, and a vertical part, the ramus. Inferior to the
second premolar teeth are the mental foramina for the mental nerves and vessels. The mental
protuberance, forming the prominence of the chin, is a triangular bony elevation inferior to the
mandibular symphysis (L. symphysis menti), the osseous union where the halves of the infantile
mandible fuse.
Lateral view of the skull
Figure 30. Skull, lateral view
http://www.arthursclipart.org/medical/skeletal/skull%20lateral%20view.gif
The lateral aspect of the cranium is formed by both the neurocranium and the viscerocranium .The
main features of the neurocranial part are the external acoustic opening, and the mastoid process
of the temporal bone. The main features of the viscerocranial part are the zygomatic arch, and
lateral aspects of the maxilla and mandible.
The zygomatic arch is formed by the union of the temporal process of the zygomatic bone and the
zygomatic process of the temporal bone.
The external acoustic opening (pore) is the entrance to the external acoustic meatus (canal),
which leads to the tympanic membrane (eardrum). The mastoid process of the temporal bone is
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posteroinferior to the external acoustic opening. Anteromedial to the mastoid process is the styloid
process of the temporal bone, a slender needle-like, pointed projection.
Posterior view of the skull (Occipital aspect of the cranium)
Figure 30. Skull, posterior view
http://www.infovisual.info/03/016_en.html
The posterior or occipital aspect of the cranium is composed of the occiput (L. back of head, the
convex posterior protuberance of the squamous part of the occipital bone), parts of the parietal
bones, and mastoid parts of the temporal bones. The external occipital protuberance, is usually
easily palpable in the median plane; however, occasionally (especially in females) it may be
inconspicuous. A craniometric point defined by the tip of the external protuberance is the inion (G.
nape of neck). The external occipital crest descends from the protuberance toward the foramen
magnum, the large opening in the basal part of the occipital bone. The superior nuchal line,
marking the superior limit of the neck, extends laterally from each side of the protuberance; the
inferior nuchal line is less distinct. In the center of the occiput, lambda indicates the junction of the
sagittal and the lambdoid sutures . Lambda can sometimes be felt as a depression. One or more
sutural bones (accessory bones) may be located at lambda or near the mastoid process.
Superior view of the skull (Superior aspect of the cranium)
Figure 31. Skull bones, superior view
http://www.becomehealthynow.com/images/organs/bones/skull_bones_top_view.png
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The superior (vertical) aspect of the cranium, usually somewhat oval in form, broadens
posterolaterally at the parietal eminences. In some people, frontal eminences are also visible,
giving the calvaria an almost square appearance.
The coronal suture separates the frontal and parietal bones, the sagittal suture separates the
parietal bones, and the lambdoid suture separates the parietal and temporal bones from the
occipital bone. Bregma is the craniometric landmark formed by the intersection of the sagittal and
coronal sutures. Vertex, the most superior point of the calvaria, is near the midpoint of the sagittal
suture.
The parietal foramen is a small, inconstant aperture located posteriorly in the parietal bone near
the sagittal suture; paired parietal foramina may be present.
CRANIAL BASE (BASE OF THE SKULL, BASICRANIUM, KAFA TABANI)
The cranial base (basicranium) is the inferior portion of the neurocranium (floor of the cranial cavity) and
viscerocranium minus the mandible. The external surface of the cranial base features the alveolar arch of
the maxillae (the free border of the alveolar processes surrounding and supporting the maxillary teeth);
the palatine processes of the maxillae; and the palatine, sphenoid, vomer, temporal, and occipital bones.
The hard palate is a part of the external surface of the cranial base.
The internal surface of the cranial base (L. basis cranii interna) has three large depressions that lie at
different levels: the anterior, middle, and posterior cranial fossae, which form the bowl-shaped floor of the
cranial cavity. The anterior cranial fossa is at the highest level, and the posterior cranial fossa is at the
lowest level.
Figure 32. Cranial base
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