Skull

  • Total bones: 22

    • Cranial bones: 8

    • Facial bones: 14

Cranial Bone Groups

  • Calvaria (roof): 4 bones

  • Cranial floor (base): 4 bones

Bones (4):

  • Frontal

  • Occipital

  • Right & Left Parietal

Bone Structure

  • Outer compact plate: Pericranium

  • Inner compact plate: Endocranium

  • Spongy bone between plates: Diploë

Bones (4):

  • Ethmoid

  • Sphenoid

  • Right & Left Temporal

Cranial Fossae (3)

Fossa

Houses

Extends

Anterior

Frontal lobes

Frontal bone → lesser wings of sphenoid

Middle

Temporal lobes

Lesser wings → petrous ridges

Posterior

Cerebellum, pons, medulla

Posterior to petrous ridges

Junctions

  • Bregma: Coronal + Sagittal

  • Lambda: Sagittal + Lambdoidal

  • Anterior: Anterior fontanel

  • Posterior: Posterior fontanel

  • Anterolateral

  • Posterolateral

  • Adult cranial size reached: ~12 years

Type

Shape

Petrous Angle

Dolichocephalic

Long, narrow, deep

40°

Mesocephalic

Average skull

47°

Brachycephalic

Short, wide, shallow

54°

Parts

  • Frontal squama: Forehead, anterior cranial vault

  • Horizontal portion: Orbits, nasal cavity roof, anterior cranial fossa

Landmarks

  • Frontal eminences

  • Supraorbital margins

  • Superciliary arches

  • Supraorbital foramina

  • Glabella

Special

  • Frontal sinuses: Between tables of squama

Articulates with

  • Parietal, sphenoid, nasal, ethmoid

Location: Between the orbits

Forms part of

  • Anterior cranial fossa

  • Nasal cavity

  • Orbits

  • Bony nasal septum

Parts

  • Cribriform plate: Olfactory nerve transmission

  • Crista galli: Midline projection

  • Perpendicular plate: Superior nasal septum

  • Labyrinths: Contain ethmoid sinuses

Labyrinth Features

  • Air cells: Anterior, middle, posterior

  • Form medial orbital walls & lateral nasal walls

  • Contain superior & middle nasal conchae

Articulates with

  • Frontal, sphenoid, lacrimal, maxilla, vomer

  • Form sides & roof of cranium

  • External surface: Convex

  • Internal surface: Concave

Landmarks

  • Parietal eminence: Skull width measurement point

Articulates with

  • Opposite parietal (sagittal)

  • Frontal (anterior)

  • Occipital (posterior)

  • Temporal

  • Sphenoid

Shape: Bat-like
Location: Central cranial base

Parts

  • Body

  • Lesser wings

  • Greater wings

  • Pterygoid processes

Body

  • Sella turcica: Houses pituitary gland

  • Tuberculum sellae: Anterior border

  • Dorsum sellae: Posterior border

  • Posterior clinoid processes

  • Clivus: Supports pons

Pituitary Location

  • MSP, ¾ in anterior & superior to EAM

Lesser Wings

  • Form orbital roofs & anterior cranial fossa

  • Contain optic canals

  • End as anterior clinoid processes

Greater Wings

  • Middle cranial fossa

  • Posterolateral orbital walls

  • Foramina: Rotundum, Ovale, Spinosum

Pterygoid Processes

  • Articulate with palatine bones & vomer

  • Pterygoid hamulus on medial plate

Articulates with: All 7 other cranial bones

Location: Posteroinferior skull

Parts

  • Squama

  • 2 Occipital condyles

  • Basilar portion

Landmarks

  • Foramen magnum: Medulla oblongata

  • External occipital protuberance (Inion)

  • Internal occipital protuberance

Foramina

  • Hypoglossal canal: Anterior to condyles

  • Condylar canals: Posterior to condyles

  • Jugular foramen: IJ vein + CN IX, X, XI

Basilar portion

  • Fuses with sphenoid → Clivus

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