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Head & Neck Anatomy

The Skull 3

Done By : Mu'ad Al-Zou'bi

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The skull is composed from twenty two bones, eight of them make the neurocranium i.e. the box that covers

the brain and the other fourteen bones form the shape of the face (the viscerocranium or the facial bones).

The cranial bones (i.e the eight bones that form the neurocranium) or the brainbox (or brain case) is divided

into the cranial vault which is the roof and the lateral walls of the neurocranium and the cranial base which

is the floor of this box, within this box the brain and the meninges (the three layers that cover the brain andprotect it) are located.

On the vault, there are three important sutures (coronal, sagittal and lambdoid) and four important

intersections or points (bregma, vertex, lambda and pterion which is the weakest and the most dangerous

point in the skull).

The cranial base from inside (internal surface) is divided into three depressions or fossae, those are the

anterior cranial fossa, the middle cranial fossa that is shaped like a butterfly, and the deepest depression is

the posterior cranial fossa (it's the deepest fossa of the three because it contains the cerebellum), the mostimportant thing is to know the openings of the foramina of each fossa (then Dr.Allouh went through these

foramina which were mentioned in the previous lectures).

The vault of the skull is formed by the process ofintramembranous ossififcation, those are flat bones (the

parietal bone, the squamous part of the occipital or temporal, the forntal etc.) so the mesenchyme can easily

turn into bone but because of the complexity of the shape of the cranial bones in the cranial base, the

intramembranous ossification cannot be done (for example, the sphenoid bone has, a body, sella turcica,

wings, legs), the mesenchyme cannot be turned directly into sphenoid bone for example.

(When we want to make a car or a plane or even a building we make a model to look where are the weak

points, we look if everything is okay then we start making or building).

So, in the cranial base bones a primary model of cartilage is done (take the petrous part of temporal bone

for example, it should be formed as a rocky mountain in shape and a cave should be made inside this

mountain to contain the middle and the inner ear) because of the complexity of the shape of these bones, if

everything is okay in the primary model, the cartilage is okay (as needed) then, in the next step the

calcification starts (this is called the endochondral ossification).

Intramembranous offsification Endochondral Ossification

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The Posterior Cranial Fossa

In the posterior cranial fossa there are four main openings, these are:

1- The foramen magnum, which is the largest foramen in the posterior cranial fossa and it's located in the

basilar part of occipital bone, at the level of foramen magnum the extent of the brain stops and the spinal

cord starts, the medulla oblongata (i.e. the lowest part of the brain) ends at the level of foramen magnum

and the spinal cord starts there, also some important structures such as the vertebral arteries (that provides

blood supply to the brain when they become cerebral arteries) pass from the foramen magnum and the

spinal accessory nerve enters the foramen magnum and leave (to be mentioned later).

2- The jugular foramen, it's located anteriolateral to the foramen magnum (jugular means related to neck),

it's called the jugular foramen because one of the largest veins that passes across the neck is arrives or starts

from the jugular foramen, this vein is the internal jugular vein (IJV), most of the veins in the neck are called

jugular (now cervical is used to mean related to neck, but the name of the vein is still jugular), the vein which

is superficial is called the external jugular vein (EJV), the deep one is the internal jugular vein, the one in

front is the anterior jugular vein. The jugular foramen is a large foramen relatively to the other openings

along with the internal jugular vein, three cranial nerves pass from this foramen, namely those are the

cranial nerve number nine, ten and eleven (CN IX = the glossopharyngeal nerve and from its name it goes to

the tongue and the pharynx, CN X = the vagus nerve, the wondering nerve, CN XI = the accessory nerve).

[Note: the nerves in the human body are divided into either spinal or cranial nerves, the spinal nerves arise

from the spinal cord, they are thirty one (31) pairs, they form networks which are called plexuses and from

these plexuses the real peripheral nerves start such as the radial, ulnar and the median nerve. The cranial

nerves are twelve (12) pairs arising directly from the brain, but not all of them arise directly from the

brain, the only exception the cranial nerve number eleven which is the accessory nerve.]

3- The hypoglossal canal, it's a small opening located in the anteriolateral border of foramen magnum, the

hypoglossal nerve (the twelfth cranial nerve, CN XII) passes from this foramen (hypo = below, glossal =

related to the tongue) this nerve goes from the brain across the hypoglossal canal and cross the neck all the

way, then it makes a U-turn and ascends and gets into the oral cavity to reach the tongue from below that's

why it's called the hypoglossal nerve since it reaches the tongue from below, this nerve innervates the

muscles of the tongue (that move the tongue).

4- The internal acoustic (or auditory that means related to audio) meatus, it's a small opening in the

posterior part of petrous temporal bone which is located anterior to the jugular foramen, a meatus is not an

opening like a foramen rather it's like a canal or passage way, this way (the internal acoustic meatus) passbetween the posterior cranial fossa and the inner ear (the ear is divided into the external ear that you can

The Depressions in Anatomy

1- When the depression is rounded, it can be either a fossa or a cavity, the difference is that the fossa with incomplete covering (the roof or the lateral walls

are open) whereas the cavity has a complete covering, the notch is located at the border of the bone whereas the fossa is located at the surface of the bone.

2- When the depression is linear, it can be a groove (e.g. the groove that is made by the passage of the middle meningeal artery as it passes over the bone), if

the linear depression becomes somewhat shallower than the groove it will be a sulcus.

The fissure is completelyopen, it's a linear communication between two spaces (e.g. the superior orbital fissure that communicates the middle cranial fossawith the orbit.

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see part of it i.e. the auricle, the middle ear and the internal ear), the middle and the inner ear are located

inside the petrous part of the temporal bone, in the ear there is an opening to the outside which is called the

external acoustic (or auditory) meatus i.e. the passage from outside and there is another one from inside,

this is the internal auditory meatus, the function of the external acoustic meatus is the collection of the

sound waves and passing them from the outside or the external to the middle ear or to the tympanicmembrane whereas the function of the internal acoustic meatus is to make a passage way for the hearing

nerve (enters from the brain to the inner ear through this meatus and transmit the nerve impulses) which is

the cranial nerve number eight (CN VIII, the vestibulocochlear nerve) also the seventh cranial nerve (CN VII,

the facial nerve) passes from this meatus.

The external surface of the cranial base has a kind of exception, there is some complexity because some

facial bones appear, those facial bones the participate in the inferior aspect of the skull are the two maxillary

bones and their alveolar processes (because it contains alveoli or sockets where the roots of the teeth are

located) which are the bony processes that hold the roots of the teeth, the palatine processes of maxillary

bones that contribute to the hard palate, the horizontal plates of palatine bones, and the vomer bone, after

those the neurocranial parts can be seen which are, parts of the sphenoid bone (the pterygoid processes and

the greater wings), parts of the temporal bone (the manidbular fossa which participate in the formation of

the temporomandibular joint or the TMJ, in this depression the head of the mandible or the mandibular

condyle rests, the styloid process which is a very sharp elevation like the writing tool or the pen, and another

elevation which is the mastoid process, this bony elevation can be felt if you put your hand behind your ear,

mastus means breast, so it looks like the breast, and the stytlomastoid foramen and the carotid canal can

Hypoglossal canal

Internal acoustic meatus

Foramen magnum

Jugular foramen

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also be seen from the inferior view of the skull), and parts of the occipital bone (the condylar part and the

basilar part).

Try to find the previous features in the following image:

Vomer bone

Horizontal plate of maxilla

Alveolar process of maxilla

Horizontal plate of palatine bone

Lateral pterygoid plate

Medial pterygoid plate

Occipital condyles

Basilar occipital bone

Carotid canal

Stylomastoid foramenMastoid process

Styloid process

Mandibualr or glenoid fossa

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The Facial Skeleton of The Skull

The facial bones are fourteen (14) in number and provide the shape of the face, these bones were

mentioned before. In the regional anatomy, we don't study the bones themselves but we study regions, so

we study the regions of the face, these are around four regions:

1- The forehead, it's made by the frontal bone (the frontal bone is a part of the neurocranial bones the more

important contribution of this bone is to protect the brain but it also participate in providing the shape of

the face), you should know two things about the forehead, the first thing is a point which is usually used in

orthodontics which is called the nasion, it's an additional intersection (remember that in the neurocraniu,

there are four intersections which are the bregma, vertex, lambda and pterion) that is located in the face not

in the neurocranium, it represents the intersection between the frontal and the nasal bones, the second

thing is the metopic suture which is located in some adults (not in everyone), metopic is a Latin word that

means the forehead, the suture is a joint, and this suture is a remnant of mesenchyme (when the

mesenchyme starts to calcify in the flat parts of the cranial vault by the process of intramembranous

ossification it turns directly into bone, in the frontal bone this process starts to calcify from the two sides in

the centers of ossification, starts in a center then it spread in a circular direction, in the frontal bone it starts

in two centers that are located at the right and the left corners, and the process of calcification grows up,

the area in the middle is the last area to close or to calcify, it remains open and contains embryonic tissue or

mesenchyme, this suture is still there after birth until the age of six (6) years because the skull keeps

growing, so as the skull grows, the suture is still there to allow for growth of the frontal bone to become

more rounded and be in the proper shape, at this time we refer to this as the frontal suture), it's normal in

the childhood, located in the median plane in the immature skull and it usually fuses (closes or ends) when

the child reaches the age of six years, in some adults it doesn't close, parts of the embryonic tissue remains

there (if the frontal suture doesn't close after six years it will be called the metopic suture).

If themetopic suture is still present, it has no significance clinically, but what is clinically significant is not the

presence of the suture, it's the disappearance of the suture (the premature closure of the frontal suture

before the age of six years), the baby is born without this suture, the calcification was at a higher speed, in

this case as the skull grows it cannot grow in a rounded way, because the frontal suture is closed, it will grow

on the sides and in front it will not grow, so the skull shape will be like a trigon (or triangular in shape), this

case is known as the trigonocephaly (trigono, from trigon, sharp angle in front and cephaly from cephalon

which means head), so trigonocephaly means head shaped like a triangle.

Frontal suture

Nasion

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2- The orbit, when we go down from the forehead, we find the orbit, it's pyramidal in shape (the pyramid

has four walls, a tip and a base), the base of the orbit is not there, it's opened to allow for the eyeball to

project to the outside, in the tip of the orbit, the optic canal is located that comes from the lesser wing of

sphenoid bone, so the optic canal is the topmost point or the tip of the pyramid, the orbit has four walls, a

superior wall (or roof)1, a lateral walls

2, an inferior wall (or floor)

3and a medial wall

4, each of these walls is

made out of two bony parts except the medial part which is made of four bony parts.

a. The roofis made of the frontal bone (orbital plate) and the lesser wing of the sphenoid bone.

b. The lateral wall is made of the zygomatic bone and the greater wing of the sphenoid bone.

c. The floor is made of the maxillary bone and part of the palatine bones.

d. The medial wall is made of the frontal process of the maxillary bone (the processes in the skull bones is

named by, where it goes and from where it comes, for example, the zygomatic process of maxillary bone,

the frontal process of zygomatic bone), the lacrimal bone on which there is a depression where the lacrimal

sac rests, the ethmoid bone and the body of sphenoid bone.

There are two fissures in the orbit which are complete cuts that communicate the orbit with other regions,

these fissure are:

I. The superior orbital fissure, it's located between the superior and the lateral walls, it separates the lateral

wall from the roof of the orbit (in other words, it's located between the greater and the lesser wings of the

sphenoid bone), this fissure communicated the orbit with the middle cranial fossa (the nerves that innervate

the muscles that move the eyeball pass from the middle cranial fossa through this fissure into the eyeball

muscles, these are the cranial nerves CN III, CN IV and CN VI).

II. The inferior orbital fissure, it's located between the floor and the lateral wall of the orbit, it

communicates the orbit with the infratemporal fossa, an incomplete space or a depression below the

temporal bone, this is the most important region for the dental professionals, everyone in dentistry should

know the complete anatomy of the infratemporal fossa because most of the structures that pass into the

teeth especially the mandibular nerve (V3) and all of its branches are located there, the veins that drain the

eyeball and the orbit pass from this fissure (infraorbital veins) to the pterygoid venous plexus (the venous

drainage of the face and the orbit pass from this fissure to the infratemporal fossa).

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Infratemporal fossa

Palatine bone Maxillary bone

Inferior orbital fissure

Greater wing of sphenoid

Zygomatic bone

Superior orbital fissure

Body of sphenoid

Ethmoid bone

Lacrimal bone

Frontal process of maxilla

Frontal bone

Lesser wing of sphenoid

Optic canal

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3-The nasal cavity, it's located between the anterior cranial fossa superiorly and the oral cavity inferiorly,

it's divided into the right and the left nasal cavities by the nasal septum, the nasal septum is made of two

bones, the superior part of it is made from the vertical or the perpendicular plate of the ethmoid bone

whereas the lower half of the nasal septum is made from the vomer bone. On the lateral walls of the nasal

cavities, there are scrolls or shelves descend from the lateral walls, those are called the conchae, thesuperior and the middle conchae are parts of the ethmoid bone whereas the inferior conchae are separate

bones by themselves, these conchae are important because they protect the openings of the paranasal

sinuses.

4- The maxillae, there are two maxillary bones contributing to the upper jaw, each maxillary bone looks

more or less pyramidal in shape and if it's fractured, you'll see that it's hollow or empty from inside, it has

the largest air sinus that's called the maxillary air sinus and sometimes when you extract the posterior upper

teeth (from the first premolar to the second molar), you'll see that the tips of the roots of these teeth

project into this space, so sometimes you open to the maxillary air sinus, after doing an extraction for the

upper first molar for example, try to put the mirror there and ask the patient to breath from his nose only,

you'll see that there will be evaporation on the mirror which indicates that the air enters through the

maxillary air sinus and goes from there, this indicates that the roots of these teeth project into this air sinus

most of the time because it's a very large air sinus.

In addition to the body of the maxilla which looks pyramidal in shape and it's empty from inside, each

maxillary bone has four (4) processes, these are the frontal process of the maxillary bone1

projects superiorly

towards the frontal bone, the one that projects laterally into the zygomatic bone is referred to as the

zygomatic process of the maxillary bone2, the one which projects inferiorly and contains sockets to hold the

roots of the teeth is called the alveolar process of the maxillary bone3, the two alveolar processes of the two

Middle concha

Inferior concha

Vomer bone

Vertical plate of etmoid

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maxillae form what's called the upper jaw, the last process projects posteriorly from the maxilla, it cannot be

seen in an anterior view but can be seen in an inferior view, this is called the palatine process of the

maxillary bone4 and it contributes to the anterior two thirds (2/3) of the hard palate.

[Note: the palate is divided into the hard and the soft palate, the anterior three quarters (3/4) of thepalate contain bone and is called the hard palate, the posterior quarter (1/4) is made of muscles and is

called the soft palate, the soft palate cannot be seen in the skull because it contains bones only, what can

be seen in the skull is the hard palate, now, the hard palate itself is divided into an anterior two thirds

(2/3) which is made from the palatine process of the maxilla and a posterior third (1/3) which is made

from the horizontal plate of the palatine bone.]

There are two important openings or foramina in the maxillary bone these are:

a. The infraorbital foramen which is located in the anterior wall below the orbit, the infraorbital nerve arises

from this foramen, the infraorbital nerve is the termination of the maxillary nerve (V2), the maxillary nervepasses from the foramen rotundum and enters the maxilla from behind, while it passes inside the maxilla, it

gives branches to the upper teeth to innervate them, then it goes from the maxilla (anteriorly) through the

infraorbital foramen and ends in the face as the infraorbital nerve to give sensation to an area of the face

(sensation to the maxillary region) and terminates there, and with this nerve there is an artery which is

called the infraorbital artery which is a branch of the maxillary artery but it's not the termination of the

maxillary artery.

b. The incisive foramen is located inferiorly within the hard palate behind the central incisors that's why it's

called the incisive foramen, it's located between the two palatine processes of the maxillae and it's very

important because the incisive nerve(part of the nasopalatine nerve) passes from this foramen and it gives

sensation to the anterior area of the palate behind the anterior teeth which is called the primary palate, on

this part of the palate the palatine rugae are located, so, the sensation in these rugae is carried by the

incisive nerve. So, the incisive nerve provides sensation to the gingivae behind the anterior teeth in the

primary palate.

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Incisive foramen

Palatine process of maxilla

Alveolar process of maxilla

Palatine ru ae

Soft palate

Hard palate

Alveolar process of maxilla

Zygomatic process of maxilla

Infraorbital foramen

Frontal process of maxilla

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5- The mandible, it's the largest and the strongest of the fourteenth facial bone and it goes all the way

across the sides (from one side to the other side), it belongs to the U-shaped bones, the U-shaped rule

bones are the bones that goes from side to side (for example, the mandible and the hyoid bones), these

bones are usually very strong, although it's very strong, it's the second most to be fractured (after the nasal

bones) because it's the only movable skull bone (there are other movable bones inside the skull, but arenot considered as skull bones, these are the ear ossicles, the bones of the middle ear that make the

vibration and are located inside the petrous part of the temporal bone, if you break the petrous part of the

temporal bone and goes to the inner and middle ear, you'll see three small bones that move inside a cavity,

these are the malleus, the incus and the stapes which is the smallest bone in the human body).

The mandible is composed of a horizontal, U-shaped part which is called the body of the mandible and it's

the largest part of the mandible and two elevations, one on each side, these are called the rami (singular,

ramus which means branch), the area where the horizontal (the body) and the vertical (the ramus) parts of

the mandible meet is called the angle of the mandible at this angle the body ends and the rami start.

At the tip of the ramus, there are a depression and two elevations, the depression is referred to as the

mandibular notch (notch = a depression on the bone border), one elevation is located anterior and the

other is posterior to this notch, the anterior one is called the coronoid process (coronoid means like a

crown) it's like a crown on the upper part of the mandible, this process is formed actually because the

largest muscle of mastication is attached there (the elevations in the bones are formed by muscle or

ligament attachment or because there is a joint in the case of a condyle for example), this muscle arise

from the side of the head around the temporal bone (the temporal area or the temple) and goes all the

way down into the coronoid process, when this muscle contracts, it elevates the mandible (try to clench

your teeth and put your fingers on the side of your head you'll feel this muscle contracted, those are the

fibers of this muscle), it's called the temporalis muscle. The process behind the mandibular notch has a

different function, this is called the condylar process because on the tip of this process there is a condyle

(the mandibular condyle), the condyle has a smooth round surface and it shares forming a joint, this

condyle enters into the mandibualr fossa of the temporal bone to form the temporomandibular joint

(TMJ), to allow for the opening and closure of the mouth, the condylar process consists of a condyle above

which is called the head of the mandible, the narrowing that occurs below the head is called the neck of

the mandible (the condylar process of the mandible is composed of the head and the neck of the

mandible).

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-.""

- I apologize for any scientific, grammatical or spelling error if it's present.

"Mu'ad Salahuddin Al-Zou'bi"

Alveolar process

Mental foramen

BodyAngle

Ramus

Neck

Head

Lingula

Mandibular foramen

Coronoid process

Mandibular notch

Condylar process

Some notes:

- The orbital cavity contains the vision system i.e. the eyeball and the lacrimal system i.e. the lacrimal

gland and the lacrimal sac.

- The nasal cavity between and below the two orbits where the nose area is.

- The oral cavity is within or between the upper jaw and the lower jaw.

- The upper jaw = two maxillary bones.

- The lower jaw = only one bone all the way around which is the mandible.

- The suture within the frontal bone is called frontal suture if it's in the child (before six years) and if it

remains after this it will be called the metopic suture (in an adult for example).

Note:

Dr.Allouh said that he is

not sure which one is

deeper the sulcus or the

groove, so try to look

for this !

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