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The Gross Anatomy of the Head and Neck:

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THE HEAD

Osteology of the skullIntroduction:• superior part of the body that is attached to the trunk by the neck

Composition:• the brain and its protective coverings, the ears, and the face

The Cranium

Introduction:• The cranium (skull) is the skeleton of the head

Parts:• has two parts: the neurocranium the viscerocranium

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Neurocranium (Cranial vault)

Introduction: • is the bony covering (case) of the brain and its

membranous coverings, the cranial meninges. • It also contains proximal parts of the cranial nerves

and the vasculature of the brain.

Parts:

The neurocranium has: • a dome-like roof called the calvaria (skullcap) • and a floor or cranial base (basicranium)

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Basicranium

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Composition:• The neurocranium in adults is formed by a series of eight

bones: Four are singular bones and the other two sets of bones occur as bilateral pairs

The four singular bones are: frontal ethmoidal sphenoidal occipital

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• While two sets of bones occurring as bilateral pairs are: Temporal parietal

note The ethmoid bone is an irregular bone that makes a relatively

minor midline contribution to the neurocranium but is primarily part of the viscerocranium

Viscerocranium (facial skeleton) • comprises the facial bones• forms the anterior part of the cranium • consists of the bones surrounding the mouth (upper and lower

jaws), nose/nasal cavity, and most of the orbits (eye sockets or orbital cavities)

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Composition:• consists of 15 irregular bones: • Three are singular bones • While 6 bones occur as bilateral pairs The three singuar bones are: Mandible Ethmoid Vomer The 6 bilateral paired bones are: Maxillae inferior nasal conchae zygomatic palatine nasal lacrimal bones

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Note:• The maxillae and mandible house the teeths• They provide the sockets and supporting bone for the

maxillary and mandibular teeth. • The Maxillae: contribute the greatest part of the upper facial skeleton, form the skeleton of the upper jaw It is fixed to the cranial base• The Mandible : forms the skeleton of the lower jaw, It is movable because it articulates with the cranial base at

the temporomandibular joints (TMJs).

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Anterior or facial(frontal) aspect of the Cranium• Features include: the frontal bone zygomatic bones orbits, nasal region, maxillae, mandible

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The frontal bone • it is a squamous (flat) part• forms the skeleton of the forehead• articulates inferiorly with the nasal and zygomatic bones. • The supraorbital margin of the frontal bone has a supraorbital

foramen (notch) for the passage of the supraorbital vessels and nerves

• Just superior to the supraorbital margin is a ridge called the superciliary arch

• Between these arches is a smooth, slightly depressed area called the GLABELLA

• The Glabella is the anterior most projecting part of the forehead• Just above the glabella is a point on the midline of the forehead called

the Ophyron• On the midline of the mandible is the the most anterior point on the

mandible which is the most prominent part of the chin. • This point is called the pogonion

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• The intersection of the frontal and nasal bones is called the NASION, a depressed area (bridge of the nose)

• The frontal bone also articulates with the lacrimal, ethmoid, and sphenoids bones

The nasal region• made up of a pair of nasal bones which are joined together at

midline by the nasal septum• Inferior to these nasal bones is a pear shaped piriform aperture• the bony nasal septum can be observed through this aperture

dividing the nasal cavity into the right and left parts• On the lateral wall of each nasal cavity are curved bony plates

called the nasal conchae

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Maxillae• form the skeleton of the upper jaw• Occur in pairs• The two maxillae are united at the intermaxillary suture in

the median plane• their alveolar processes include the tooth sockets (alveoli) and

house the maxillary teeth • They articulate with the frontal bone anteriorly and zygomatic

bones laterally • On the body of the maxilla is the infraorbital foramen for

passage of the infraorbital nerve and vessels

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Mandible• is a U-shaped bone • forms the skeleton of the lower jaw• Its alveolar process supports the mandibular teeth. consists of: of a horizontal part (the body) and a vertical part (the ramus )• Inferior to the second premolar teeth are the mental

foramina for the passage of the mental nerves and vessels• The base of the mandible has a midline swelling called the

mental protuberance• Lateral to the mental protuberance on either side is a slightly

more pronounced bumps called the mental tubercles

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Zygomatic Bone• Also known as cheek bone, malar bones• On the lateral aspect of this bone is a foramen called the

zygomaticofacial foramen• this foramen allows for the passage of the zygomaticofacial

nerve• This bone articulates with the frontal, sphenoidal, maxillae and

temporal bones

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Clinical anatomy Injury to the superciliary arches• The superciliary arches are relatively sharp bony ridges;

consequently, a blow to them (e.g., during boxing) may lacerate the skin and cause bleeding. Bruising of the skin surrounding the orbit causes tissue fluid and blood to accumulate in the surrounding connective tissue, which gravitates into the superior (upper) eyelid and around the eye

Malar Flush• The zygomatic bone was once called the malar bone.• Clinically the term malar flush refers to redness of the skin

covering the zygomatic prominence (malar eminence), which is associated with a rise in temperature in various fevers occurring with certain diseases, such as tuberculosis

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Superior aspect of the skull• Also called the calvaria or skull cap• Bones forming it include Frontal bone (unpaired) Paired parietal bones Occipital bone (unpaired)• The outer surface of the skull possess a number of landmarks The frontal bone articulates with the paired parietal bones at

the coronal suture The two parietal bones articulate with each other at the

sagittal suture The paired parietal bones articulate with the occipital bones at

the lambdoid suture

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The junction(intersection) between the coronal and sagittal sutures is called the bregma

The junction(intersection) between the sagittal suture and lambdoid sutures is called the lambda

The vertex is the most superior point of the skull near the midpoint of the sagittal suture

The parietal foramen on the parietal bone is variable, and it allows for the passage of emissary veins

Obelion: The region of the skull between the two parietal foramina where the closure of the sagittal suture usually begins

Clinical Anatomy

Fracture of the Calvaria Depressed fractures: this can results from hard blows in thin areas of the calvaria in

which a bone fragment is depressed inward, compressing and/or injuring the brain

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Linear calvarial fractures : the most frequent type usually occur at the point of impact; but fracture lines often radiate away

from it in two or more directions Comminuted fractures: the bone is broken into several pieces. If the area of the calvaria is thick at the site of impact, the bone may bend

inward without fracturing; however, a fracture may occur some distance from the site of direct trauma where the calvaria is thinner

Contrecoup (counterblow) fracture: no fracture occurs at the point of impact, but one occurs on the opposite

side of the cranium

Obliteration of the Cranial Sutures• The obliteration of sutures between the bones of the calvaria usually begins

between the ages of 30 and 40 years on the internal surface and approximately 10 years later on the external surface

• Obliteration of sutures usually begins at the bregma and continues sequentially in the sagittal, coronal, and lambdoid sutures

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Skull of a newborn baby• The halves of the frontal bone in the newborn are separated by the

frontal suture• the frontal and parietal bones are separated by the coronal suture• and the maxillae are separated by the intermaxillary suture • mandible consists of two halves united in the median plane by

the mandibular symphysis • this union begins during the 1st year and the halves are fused by

the end of the 2nd year• No mastoid process at birth• No styloid process • The mastoid processes form gradually during the 1st year• The bones of the calvaria of a newborn infant are separated by

membranous intervals called frontanelles

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• They include: anterior fontanelle posterior fontanelle paired sphenoidal fontanelle Paired mastoid fontanelles

Anterior fontanelle • intro: the largest frontanelle• shape: diamond or star shaped• boundary: bounded by the halves of the frontal bone anteriorly and the

parietal bones posteriorly. • Location: at the junction of the sagittal, coronal, and frontal sutures, the

future site of the bregma • closure: By the 18 months of age, the surrounding bones have fused and the

anterior fontanelle is no longer clinically palpable

Frontal bone of a newborn• Union of the halves of the frontal bone begins in the 2nd year• In most cases, the frontal suture is obliterated by the 8th year• in approximately 8% of people, a remnant of the frontal suture persist called

the metopic suture

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Posterior fontanelle • Shape: is triangular • boundary: bounded by the parietal bones anteriorly and the

occipital bone posteriorly• location: at the junction of the lambdoid and sagittal sutures, the

future site of lambda • Closure: 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

Sphenoidal and mastoid fontanelles• overlain by the temporal muscle, • fuse during infancy and are less important clinically than the

midline fontanelles note• The halves of the mandible fuse early in the 2nd year• The two maxillae and nasal bones usually do not fuse

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Molding of the calvaria• The softness of the cranial bones in infants and their loose connections

at the sutures and fontanelles enable the shape of the calvaria to change (mold) during birth

• During passage of the fetus through the birth canal, the halves of the frontal bone become flat, the occipital bone is drawn out, and one parietal bone slightly overrides the other

• Within a few days after birth, the shape of the calvaria returns to normal

• 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

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Craniosynostosis and Cranial Malformations

• Premature closure of the cranial sutures is called craniosynostosis results in several cranial malformations

• Premature closure of the sagittal suture, in which the anterior fontanelle is small or absent, results in a long, narrow, wedge-shaped cranium, a condition called scaphocephaly

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• When premature closure of the coronal or the lambdoid suture occurs on one side only, the cranium is a condition known as plagiocephaly

• Premature closure of the coronal suture results in a high, tower-like cranium, called oxycephaly or turricephaly

• oxycephaly or turricephaly is more common in females Note: Premature closure of sutures usually does not affect brain

development

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Lateral aspect of the skull This includes : lateral part of the neurocranium Lateral part of the viscerocranium (facial skeleton)

Composition:• bones forming the lateral portion of the neurocranium include: the

frontal, parietal, occipital, sphenoid, and temporal bones• bones forming the visible part of the facial skeleton include the nasal,

maxilla, and zygomatic bones and the mandible• The main features of the neurocranial part are the temporal fossa, the

external acoustic opening, and the mastoid process of the temporal bone

• The main features of the viscerocranial part are the infratemporal fossa, zygomatic arch, and lateral aspects of the maxilla and mandible

The junction where the frontal, parietal, sphenoid(greater wing) and temporal bone meet is called the pterion

• It is usually indicated by an H-shaped formation of sutures

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Clinical anatomy• The pterion is an important area because it overlies the middle

meningeal artery• Fracture to the pterion can rupture the anterior branch of this

artery resulting in hematoma which exerts pressure on the underlying cerebral cortex

• An untreated meningeal artery can cause hemorrhage which can lead to death in a few hours

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The temporal bone of the lateral aspect of the skull

It has: a squamous part which articulates with the greater wing of sphenoid

at the sphenosquamous suture a zygomatic process which articulates with the zygomatic bone to

form the zygomatic arch a tympanic part which has the external acoustic meatus a petromastoid part which is usually separated into the petrous and

mastoid part• A large bony prominence projects from the inferior border of the

mastoid part of the temporal bone called the mastoid process• Medial to the mastoid process is the styloid process which projects

from the lower border of the temporal bone• The point where the superior temporal line cuts the coronal suture is

called the stephanion• While the located at junction of three sutures: parietomastoid,

occipitomastoid, and lambdoid is called the asterion

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Posterior aspect of the skull

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Bones include:• Occipital bone• Parts of the parietal bones• Temporal bones (mastoid part)

Occipital bone The occipital bone is separated from the paired parietal bone

by the lambdiod suture Along the lambdoid suture are small bones called sutural or

wormian bones there is a midline projection called the external occipital

protuberance Curved lines extend laterally from this projection called the

superior nuchal lines The most prominent part of the external occipital protuberance

is the inion

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About 1 inch (2.5cm) below the nuchal lines are additional 2 lines called the inferior nuchal lines which curves laterally

Extending downwards from the external occipital protuberance is the external occipital crest

In between the mastoid and the occipital in is the occipitomastoid suture

Note Obliteration of Cranial Sutures• The obliteration of sutures between the bones of the calvaria

usually begins between the ages of 30 and 40 years on the internal surface and approximately 10 years later on the external surface

• Obliteration of sutures usually begins at bregma and continues sequentially in the sagittal, coronal, and lambdoid sutures

The region of the skull between the 2 parietal foramina where the closure of the sagittal suture begins is called the OBELION

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CraniometricPoints of thecranium

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The Internal surface of the cranial base (cranial cavity/fossae) • has three large depressions that lie at 3 different levels: anterior crania fossa middle cranial fossa posterior cranial fossa• These form the bowl-shaped floor of the cranial cavity • The anterior cranial fossa is at the highest level(shallowest) • while the posterior cranial fossa is at the lowest level(deepest) Sitting on the floor of the anterior cranial fossa is the frontal lobes

of the cerebral hemisheres Sitting on the floor of the lateral portion of the middle cranial fossa

is the temporal lobe, and in the midline of the middle crania fossa is the pituitary gland

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Sitting on the anterior portion of the floor of the posterior cranial fossa is the brainstem (midbrain, pons and medulla oblongata) and occupying the rest of the posterior cranial fossa are the cerebellar hemispheres

Note: the occipital lobe do not sit on the floor of the posterior cranial fossa, it is the cerebellum that sit of the floor of the posterior cranial fossa

Anterior cranial fossa

Introduction:• Shallowest of the 3 cranial fossae• Lodges the frontal lobe of the brain

Bony formation:• Formed by 3 bones, namely: Frontal bone in the anterior and lateral directions Ethmoid bone in the middle portion 2 parts of the sphenoid bone in the posterior portion

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• The part of the frontal bone in the anterior cranial fossa is the orbital part/orbital surface

• The ethmoid bone of the anterior cranial fossa is made up of : A ridge which projects superiorly called the crista galli And a sieve- like cribriform plate of ethmoid which lies on each

sides of this ridge• The 2 parts of the sphenoid bone in the anterior cranial fossa

are: The jugum The lesser wing of sphenoid

Foramen The cribriform plate of ethmoid has numerous tiny foramina that

transmit olfactory nerves (CN 1) from the olfactory area of the nasal cavity to the olfactory bulb of the brain

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• The frontal bone also has a bony median extension called the frontal crest, at the base of the frontal crest is the foramen cecum

• This foramen varies in size in different individuals, and is frequently impervious; when open, it transmits the emissary vein from the nose to the superior sagittal sinus

• This has clinical importance in that infections of the nose and nearby areas can be transmitted to the meninges and brain

• Each lesser wing widens, curves posteriorly, and ends as a rounded anterior clinoid process

• Just anterior to each anterior clinoid process is a circular opening in the lesser wing of the sphenoid called the optic canal

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• The optic canal allows for the passage of ophthalmic artery and optic nerve [CN II] to pass through as they exit the cranial

cavity to enter the orbit

Note: The optic canals are usually included in the middle cranial fossa

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Middle crania fossa• It is butterfly shaped separating the anterior and middle cranial fossae are the sharp

sphenoidal crests laterally and the sphenoid limbus centrally The sphenoid limbus forms the posterior boundary of the jugum and

the anterior boundary of the prechiasmatic sulcus (note: the prechiasmatic sulcus is bounded posteriorly by the

tuberculum sellae) The prechiasmatic sulcus is a smooth groove stretching between the

optic canals across the body of the sphenoid

Bony formation• Formed mainly by the:

i. Parts of the sphenoid bone

ii. Parts of the temporal bone The parts of sphenoid involved are:

i. Sella turcica which is part of the body of sphenoid

ii. greater wings of sphenoid laterally

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Sella turcica• Has 3 parts:

i. an anterior wall called the turberculum sella

ii. a posterior wall called the dorsum sella

iii. a deep central part lying in between the turberculum sella and dorsum sella

This central part is called the hypophyseal fossa, which houses the pituitary gland

• On each side of the body of the sphenoid are four foramina perforating the roots of the greater wings of the sphenoid, these include :

i. Superior orbital fissure: a diagonal gap that separates the greater wing from the lesser wing of sphenoid

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• This fissure allows for the passage of the: Cranial nerves III, IV and VI (occuomotor, trochlear and

abducens nerves) Ophthalmic division of trigerminal nerve (CN V1)

ophthalmic vein

ii foramen rotundum: allows for the passage of the maxillary division of the trigeminal nerve (CN V2)

iii foramen ovale: allows for the passage of the mandibular division of the trigeminal nerve (CN V3)

iv foramen spinosum: allows for the passage of the middle meningeal artery and the meningeal branch of mandibular nerve

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Parts of the temporal bone include: squamous part of the temporal bones laterally and the petrous part of the temporal bones posteriorly • On the petrous part are grooves for both the greater and lesser

petrosal nerves • Posterolateral to the hypophyseal fossa is the foramen lacerum,• In life, it is closed by a cartilage plate• Only some meningeal arterial branches and small veins are

transmitted vertically through the cartilage• 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

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Posterior cranial fossa• Largest and deepest of the 3 cranial fossa• Lodges the brainstem (medulla oblongata, pons and midbrain)

and the cerebellum• Formed mainly by the occipital bone and the temporal bone• There is a slope that extend down from the dorsum sellae

leading to the foramen magnum called the clivus• posterior to the foramen magnum are cerebellar fossae which

accommodate the cerebellar hemispheres• The cerebellar fossae are partly divided by the internal

occipital crest into bilateral concave impression• The internal occipital crest ends superiorly in a bony

prominence called the internal occipital protuberance

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Grooves and foramen in the posterior cranial fossa• internal acoustic meatus: passage of facial nerve (CN VII) and

vestibulochear nerve (CN VIII)• Jugular foramen: allows the passage of: 3 cranial nerves pass through it, which are cranial nerves IX, X

and XI {glossopharyngeal,vagus and accessory nerve} 2 important venous structures, the dura venous sinuses, coming in

from the posterior side is the sigmoid sinus and from the anterior side is the inferior petrosal sinus

Note: these two sinuses enter the jugular foramen and when they emerge from the other side, they fuse together and once fused together, they are called the internal jugular vein

• hypoglossal canal: located superior to the anterolateral margin of the foramen magnum and allows for the passage of the hypoglossal nerve {CN XII}

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• Foramen magnum: allows for the passage of; The spinal cord which is continuous with the medullar

obongata The two vertebral arteries The spinal contribution of accessory nerve, the spinal

accessory nerve

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