The Skull

The Skull is formed by cranial and facial bone

Cranium

A hollow cavity in the skull that protects the brain composed of 8 cranial bones

Cranial bones

The cranium is composed of 8 bones

• Frontal bone

• Protects the frontal lobe of the brain

• Parietal bone (Left and Right)

• Forms the superior and lateral aspects of the skull

• Occipital bone

• Forms the posterior aspect and most of the base of the skull

• Ethmoid bone

• Contributes to the anterior cranial fossa

• Forms part of the nasal septum and the nasal cavity

• Contributes to the medial wall of the orbit

• Temporal bones (Left and Right)

• Forms the inferolateral aspects of the skull and contributes to the middle cranial fossa

• Each has a squamous, tympanic, and petrous part

• Sphenoid bone

• Bat-shaped bone that is described as the keystone bone of the cranium because it articulates with all other cranial bones

Sutures

Seams that connect skull bones to one another

Lambdoid suture

Coronal suture

Sagittal suture

Squamous suture

Occipitomastoid suture

Frontal bone structures

Forms the forehead, superior part of the orbit, and the floor of the anterior cranial fossa

• Squamous part

• Supraorbital margin

• Thick margin of the eye socket that lies beneath the eyebrows

• Supraorbital foramen (notch)

• Opening above each orbit allowing blood vessels and nerves to pass

• Glabella

• Smooth area between the eyes

Occipital bone structures

Forms the posterior aspect and most of the base of the skull

• Foramen magnum

• Large opening in the base of the bone, which allows the spinal cord to join with the brain stem

• Occipital condyles

• Rounded projections lateral to the foramen magnum that articulate with the first cervical vertebra (atlas)

• Hypoglossal canal

• Opening medial and superior to the occipital condyle through which cranial nerve XII (the hypoglossal nerve) passes

• External occipital protuberance

• Midline prominence posterior to the foramen magnum

• Superior nuchal line

Ethmoid bone structures

• Contributes to the anterior cranial fossa

• Forms part of the nasal septum and the nasal cavity

• Contributes to the medial wall of the orbit

• Cribriform plates

• Located lateral to the crista galli

• Form a portion of the roof of the nasal cavity and the floor of the anterior cranial fossa

• Cribriform (olfactory) foramina

• Tiny holes in the cribriform plates that allow for the passage of filaments of cranial nerve I (olfactory nerve)

• Crista galli

• “Rooster’s comb”

• A superior projection that attaches to the dura mater, helping the secure the brain within the skull

• Perpendicular plate

• Inferior projection that forms that superior portion of the nasal septum

• Lateral masses

• Flank the perpendicular plate on each side and filled with sinuses called ethmoidal air cells

• Middle nasal concha

• Extend medially from the lateral masses

• Act as turbinates to improve airflow through the nasal cavity

Temporal Bone structure

• Forms the inferolateral aspects of the skull and contribute to the middle cranial fossa

• Each has squamous, tympanic and petrous parts

• Squamous part

• Located inferior to the squamous suture

• The next two markings are located in this part

• Zygomatic process

• A bridge-like projection that articulates with the zygomatic bone to form the zygomatic arch

• Mandibular fossa

• Located on the inferior surface of the zygomatic process

• Receives the condylar process of the mandible to form the temporomanidubular joint

• External acoustic meatus

• Canal leading to the middle ear and eardrum

• Styloid process

• Needle-like projection that serves as an attachment point for ligaments and muscles of the neck

• ++This process is often missing from demonstration skulls because it has broken off++

• Mastoid process

• Located posterior to the external to the external acoustic meatus

• Serves as an attachment point for neck muscles

***

• Jugular foramen

• Located where the petrous part of the temporal part of the temporal bone joins the occipital bone

• Forms an opening which the internal jugular vin and cranial nerves IX, X, and XI pass

• Carotid canal

• Opening through which the internal carotid artery passes into the cranial cavity

• Internal acoustic meatus

• Foreamen lacerum

• Almost completely closed by cartilage in the living person but forms a jagged opening in dried skulls

• Stylomastoid foramen

• Tiny opening between the mastoid and styloid processes through which cranial nerve VII leaves the cranium

Sphenoid bone structure

Bat-shaped bone that is described as the keystone bone of the cranium because it articulates with all other cranial bones

• Body

• Greater wing

• Project laterally from the sphenoid body, forming parts of the middle cranial fossa and the orbits

• Lesser wing

• From parts of the floor of the anterior cranial fossa and part of the orbit

• Pterygoid proccess

• Project inferiorly from the greater wings n

• Attachment site for chewing muscles

• Pterygoid muscles

• Hypophyseal fossa (aka sella turcica)

• “Turkish saddle”

• Located in the superior surface of the body

• The seat of the saddle, called the hypophyseal fossa, holds the pituitary gland

• Optic canal

• Openings in the base of the lesser wings

• Cranial nerve II (optic nerve) passes through to serve the eye

• Foramen ovale

• Openings located posterolateral to the foramen rotundum

• A brancg of cranial nerve V (mandibular division) passes through

• Foramen rotundum

• Openings located in the medial part of the greater wing

• A branch of cranial nerve V (maxillary division) passes through

• Foramen spinosum

• Openings located posterolateral to the foramen spinosum

• Provides passageway for the middle meningeal artery

• Superior orbital fissure

• Slits in the orbits providing passaging of cranial nerves that control eye movements (III, IV, VI, and the ophthalmic division of V)

Face

The face makes up the anterior portion of the skull

Facial bones

The bones is composed of 14 bones

• Mandible

• The lower jawbone, which articulates with the temporal bone to form the only freely moveable joints in the skull (the temporomandibular joint)

• Maxillary bones (Left and Right)

• Keystone facial bones because they articulate with all other facial bones except the mandible

• Form the upper jaw and parts of the hard palate, orbits, and nasal cavity

• Lacrimal bones (Left and Right)

• Each forms part of the medial orbit in between the maxilla and ethmoid bone

• Zygomatic bones (Left and Right)

• Commonly called the cheekbones

• Each forms part of the lateral orbit

• Nasal bones (Left and Right)

• Small rectangular bones forming the bridge of the the nose

• Palatine bones (Left and Right)

• Forms the posterior hard palate, a small part of the nasal cavity, and part of the orbit

• Inferior nasal conchae (Left and Right)

• Inferior turbinate

• Each forms part of the lateral walls of the nasal cavities

• Improves the airflow through the nasal cavity

• Vomer

• Thin

• Blade-shaped bone that forms the inferior nasal septum

Maxilla structures

Keystone facial bones because they articulate with all other facial bones except the mandible form the upper jaw and the hard palate, orbits, and nasal cavity

• Anterior nasal spine

• Palatine process

• Forms the anterior hard palate

• Meet anteriorly in the inter-maxillary suture

  • ++Seen in the inferior view++

• Zygomatic process

• Articulation process for zygomatic bone

• Inferior orbital fissure

• Infraorbital foramen

• Opening under the orbit that forms a passageway for the for the infraorbital artery and nerve

• Alveolar process

• Inferior margin of the maxilla

• Contains sockets in which the teeth lie

• Frontal process

• Forms the part the lateral aspect of the bridge of the nose

Mandible structures

The lower jawbone, which articulates with temporal bone to form the only freely moveable joints in the skull (the temporomandibular joint)

• Body

• Horizontal portion that forms the chin

• Ramus

• Vertical extension of the body

• Condylar process

• Articulate with the mandibular fossae of the temporal bone

• Mandibular notch

• Separate the condylar process and the coronoid process

• Coronoid process

• “Crown-shaped” portion of the ramus for muscle attachment

• Alveolar process

• Superior margin of the mandible

• Contains sockets in which the teeth lie

• Mental foramen

• Mental foramina (openings)

• Paired openings on the body (lateral to the midline)

• Transmit blood vessels and nerves to the lower lip and skin of the chin

• Mandibular foramen

• Located on the medial surface of each ramus

• Passageway for the nerve involved in tooth sensation

• (Dentists inject anesthetic into this foramen before working on the lower teeth)

• Mandibular angle

• Posterior points where the ramus meets the body

• Hyoid bone

• Only bone in the body that does not articulate directly with another bone

• Found in the neck, below the mandible

• Paranasal sinuses

• Some skull bones contain air-filled cavities

• Found in five bones

  • Frontal

  • Sphenoid

  • Ethmoid

  • and each Maxilla