Human Anatomy: Bones of Skull

Skull Bones

• The skull is composed of several bones united at immobile joints called sutures, except for the mandible which is united with the skull by a mobile temporomandibular joint.
• The skull has two main functions: protecting the brain, meninges, and cerebral vasculature, and supporting the soft tissues of the face.

Cranium (Neurocranium)

• The cranium is divided into 8 bones: frontal, occipital, sphenoid, ethmoid, 2 temporal, and 2 parietal bones.
• Cranium protects the brain, meninges, and cerebral vasculature.
• Anatomically, the cranium can be subdivided into:
  • Cranial roof (Calvarium or Cranial Vault): composed of frontal, occipital, and 2 parietal bones.
  • Cranial base: composed of 6 bones: frontal, sphenoid, ethmoid, occipital, parietal, and temporal bones.

Facial Bones (Viscerocranium)

• The facial bones support the face and house the orbits, nasal, and oral cavities.
• The facial bones consist of 14 bones.

Frontal Bone

• The frontal bone forms the forehead, roof of the orbit, and nasal cavity.
• Landmarks of the frontal bone:
  • Glabella: a prominence located between the two arches.
  • Supraorbital notch or supraorbital foramina: where the supraorbital vessels and nerve pass through.
  • Zygomatic processes: arise from the squamous part and articulate with the zygomatic bones.
  • Maxillary processes: arise from the squamous part and articulate with the maxilla.
  • Frontal air sinuses: just above the orbital margins, communicating with the nose and serving as voice resonators.

Parietal Bones

• The parietal bones form the sides and roof of the cranium (bulk of calvaria).
• Articulation:
  • At sagittal suture: articulate with each other in the midline.
  • With frontal, occipital, temporal, and sphenoid bones.

Temporal Bones

• The temporal bones articulate with the facial bones, mandible, and the 1st cervical vertebra (atlas).
• Landmarks of the temporal bones:
  • Mastoid process: an inferior projection of bone, palpable just behind the ear.
  • Zygomatic process: a bony projection arising anteriorly, articulating with the temporal process of the zygomatic bone.
  • Petrous part: contains the inner ear, with two foramina: carotid canal (internal carotid artery passes through) and internal auditory meatus.
  • Styloid process: located immediately underneath the opening of the external auditory meatus.
  • Mandibular fossa: a small fossa lying inferiorly in the temporal bone for articulation with the mandible.

Occipital Bones

• The occipital bone is a single triangular bone that articulates with the sphenoid, parietal, temporal bones, and the 1st cervical vertebra (atlas).
• The occipital bone is composed of:
  • Cribriform plate: forms the roof of the nasal cavity and contains olfactory foramina which pass by olfactory nerve fibers.
  • Crista galli: arises superiorly from the cribriform plate, providing an attachment for the falx cerebri.
  • Perpendicular plate: a bony projection descending from the cribriform plate, forming the superior 2/3 of the nasal septum.

Ethmoid Bones

• The ethmoid bone is composed of:
  • Cribriform plate: forms the roof of the nasal cavity and contains olfactory foramina which pass by olfactory nerve fibers.
  • Crista galli: arises superiorly from the cribriform plate, providing an attachment for the falx cerebri.
  • Perpendicular plate: a bony projection descending from the cribriform plate, forming the superior 2/3 of the nasal septum.
  • Ethmoidal labyrinths: large lateral masses containing ethmoid air sinus.

Face

• The face is composed of:
  • Zygomatic bones: paired bones, often referred to as cheekbones, articulating with the frontal, great wing of the sphenoid, temporal, and maxillary bones.
  • Nasal bones: two slender bones located at the upper middle part of the face, forming the upper 1/3 of the nose.
  • Vomer bone: a single bone, lying vertically in the midline of the nasal cavity, forming the posterior aspect of the nasal septum.
  • Inferior nasal conchae: two bones located in the lateral wall of the nasal cavity, helping in humidification, heating, and filtering of the air inhaled through the nose.
  • Palatine bones: two bones located in the posterior part of the oral cavity, each having 2 plates: horizontal and perpendicular.