Anatomy of the skull

Dr Rania Gabr

Objectives1.List the bones of the skull

2.Identify the major sutures of the skull

3.Identify the major surface markings of the skull

4.Identify the major foramina in the skull

5.List the major structures which pass through the foramina

6.Describe the cranial fossa and its part

7.Understand the base of the skull and its fracture

8.Describe the structure of the mandible

The Skull

• It consists of flat and irregular bones

• It is divided into:

Cranial bones which encase the brain (Neurocranium)

Facial bones which form the bones of the face (Viscerocranium)

• Cranial bones include: (Neurocranium) Frontal 1 Ethmoid 1 Sphenoidal 1 Occipital 1

Parietal 2Temporal 2

• Facial bones include: (Viscerocranium)

Maxilla 2Zygomatic 2Nasal 2Palatine 2

Lacrimal 2 Inferior conchae 2

Vomer 1Mandible 1

The Skull

The Skull

• Frontal• Maxilla• Zygomatic• Nasal• Mandible• Lacrimal

• z

The Skull

• Parietal• Temporal

SquamousMastoidStyloidTympanicPetrous

• SphenoidGreater wingLesser wingPterygoid processBody

• Occipital

The Skull

• Petrous part of temporal• Lesser wing of sphenoid• Body of sphenoid• Pterygoid process• Ethmoid bone

Crista galliCribriform platePerpendicular plate

• Vomer • Palatine bone

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Frontal Bone• Landmarks:

– Squama: flat portion that forms the forehead

– Supraorbital margin: ridge under the eyebrow, forming the upper part of the orbit (eye socket)

– Supraorbital foramen: small hole within supraorbital margin for blood vessels and nerves

– Frontal sinuses: hollow spaces behind the squama, act as sound chambers to give the voice resonance.

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Frontal Bone (Anterior View) (Blue Colored Bone)

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Frontal Bone (Lateral View) (Blue Colored Bone)

Temporal bone

Temporal bone• Landmarks:

– Squama: flat portion of the temporal bone forming the anterior and superior part of the temple

– Zygomatic process: process forming part of the cheek– Petrous portion: internal,between the sphenoid and occipital,

forming part of the floor of the cranium. Contains the ear canal and internal ear structures.

– Mandibular fossa: socket between squama and petrous portion, articulates with the condyle of the mandible (TMJ)

– External auditory meatus: opening to the ear canal– Mastoid process: bony prominence behind the external auditory

meatus– Styloid process: looks like an elephant’s tusk located between the

mastoid process and the jaw. Acts as a point of attachment for muscles and ligaments.

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Temporal Bone (Lateral View) (Purple Colored Bone)

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Occiput

• Landmarks:– Foramen magnum: large

hole, allowing passage of the spinal cord

– External occipital protuberance (EOP): prominent projection on back of occiput

– Nuchal lines: a superior and inferior line running laterally from the midline, serve as a point of muscle attachment

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Occipital Bone (Lateral View) (Orange Bone)

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Occipital Bone (Posterior View) (Orange Colored Bone)

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Sphenoid Bone

Sphenoid bone• A prominent, irregular, wedge-shaped bone at the base of the skull.

The sphenoid bone has been called the "keystone" of the cranial floor since it is in contact with all of the other cranial bones.

• Landmarks– Greater wings: large lateral projections of bone that help to form

the lateral border of the skull

– Lesser wings: smaller lateral projections of bone above the greater wings

– Pterygoid processes: two long downward projections from the greater wings that act as a point of muscle attachment.

– Sella turcica: known as the Turkish Saddle which cradles the pituitary gland.

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Sphenoid Bone (Lateral View) (Green Colored Bone)

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Sphenoid Bone (Floor of Cranium) (Green Colored Bone)

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Ethmoid Bone• An irregularly shaped, spongy bone that

provides the floor of the front part of the skull and the roof of the nasal cavity.

• The ethmoid consists of two masses of thin plates enclosing air cells and looks like a sieve.

• Landmarks:– Lateral masses: form most of the wall

between the nasal cavity and the orbits– Perpendicular plate: forms the superior

portion of the nasal septum– Cribriform plate: forms the roof of the

nasal cavity– Olfactory foramina: small holes within

the cribriform plate for passage of the first cranial nerve (for smell)

– Crista galli: upward extension of bone above the cribriform plate, acts as an anchoring point for one of the coverings of the brain. ( Falx cerebi)

– Nasal conchae (turbinates): two scroll-shaped projections (superior and middle) with a mucus membrane on either side of the nasal septum. Function to cause air turbulence and trap inhaled particles.

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Bones of the faceMaxilla

• The second largest bones of the face, after the mandible and form, by their union, the whole of the upper jaw.

• They hold the upper teeth, and connect on the left and right to the zygomatic bones (cheek bones).

• Each assists in forming the boundaries of three cavities, namely, the 1-roof of the mouth, 2-the floor and lateral wall of the nose, and 3- the floor of the orbit.

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Maxilla

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Landmarks:

Infra Orbital foramen: hole below the orbit, for blood vessels and nerves

Alveolar process: arch of the maxilla

containing the upper teeth

Palatine process: horizontal projection of the maxilla forming the anterior ¾ of the hard palate.

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Zygomatic Bones

Commonly referred to as the cheekbone.

It is situated at the upper and lateral part of the face: it forms the prominence of the cheek and part of the lateral wall and floor of the orbit. It articulates with thezygomatic arch of the temporal bone.

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Vomer

One of the unpaired facial bones of the skull.

Located in the midsagittal line, and attaches to the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.

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Inferior Nasal Conchae

Extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone, curled upon itself like a scroll.

Inferior Nasal Conchae

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Lacrimal BonesSmallest and most fragile

bone of the face, is situated at the front part of the Medial of the orbit.

Contains the lacrimal sac and the naso-lacrimal duct.

Lacrimal bone

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Nasal 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

Cranial Fossa

• It is the cavity of the skull

• Divides into: Anterior cranial fossa Middle cranial fossa Posterior cranial fossa

Anterior Cranial Fossa

• Formed of: Orbital plate of frontal bone Cribriform plate of ethmoid Crista galli Lesser wing of sphenoid

• Occupied by: Frontal lobe of the cerebrum Optic nerves Olfactory bulb and tract

Middle Cranial Fossa

• Formed of: Greater wing of sphenoid Body of sphenoid Squamous part of temporal bone Anterior part of petrous bone

• It occupied by: Temporal lobe of the cerebrum

Posterior Cranial Fossa

• Formed of: Sphenoid part of clivus Posterior part of petrous bone Occipital bone• It shows the following land marks: Groove for transverse sinus Groove for sigmoid sinus Internal occipital protuberance• It is occupied by: Cerebellum Brain stem

Base of The Skull

• Most of the bones are seen in other views

Foramina of the Skull

• Foramina are found within the skull bones• They vary in size and shape• They transmit nerves, blood vessels and dura matter

Foramina of the Skull

Foramina of the Skull

• Supraorbital• Infraorbital• Mental

• The following must be identified:

Nasion Inion Bregma Lambda External occipital protuberance Parietal eminence Zygomatic arch

Sutures of the Skull

• Sutures are fibrous joints articulating the skull bones

• They include: Coronal Sagittal Lambdoid Pterion

Skull Fontanelles• Fontanelles are spaces between some of

the skull bones of infants.• They permit easy growth of the brain.• They permit overlapping of skull bones

during labor.• They include:

1. Anterior Fontanelle Lies between Frontal and Parietal

Bones Closed by 18 months of age

2. Posterior Fontanelle Lies between Parietal and Occipital

Bones Closed by end of 1st year

3. Anterolateral Fontanelle

4. Posterolateral Fontanelle

The Mandible

• It is a flat bone• Identify the following: Head(condylar process) Mandibular notch Coronoid process Ramus Angle Body Mylohyoid line Submandibular fossa Digastric fossa Mandibular foramen Mental foramen

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