Anatomy of the Occipital and Frontal Bones

Introduction to the Skeleton System

• The skeleton is a complex bony structure.
• The skeleton consists of two major divisions: axial and appendicular.

Divisions of the Skeleton

• Axial Skeleton
  • Skull
    • 22 bones and 6 auditory ossicles
    • Protects brain and special senses
    • Provides attachment for structures that take air, food, and water.
    • The skull is made up of several cavities.
      • Cranial cavity
      • Nasal cavity
      • Orbits
      • Paranasal sinuses
      • Ears
  • Hyoid bone
  • Vertebral column
  • Thoracic (rib) cage
• Appendicular Skeleton
  • Limbs
  • Girdles

Skull (Axial Skeleton)

• 22 Bones plus 6 auditory ossicles that function in hearing.
• Two portions:
  • 1- Neurocranium (brainbox)
    • Surrounds and protects brain
    • Provides muscle attachment
    • Contains sinuses to reduce weight of the skull
  • 2- Viscerocranium (facial bones)
    • Shapes the face
    • Protects major sensory organs like eyes, nose, and tongue
    • Provides attachment for muscles of mastication, facial expression, and eye movement
• Bone List
  • Neurocranium Bones (Cranium):
    • Frontal (1)
    • Parietal (2)
    • Occipital (1)
    • Temporal (2)
    • Ethmoid (1)
    • Sphenoid (1)
  • Viscerocranium Bones:
    • Inferior nasal concha (2)
    • Lacrimal (2)
    • Vomer (1)
    • Nasal (2)
    • Zygomatic (2)
    • Palatin (2)
    • Maxilla (2)
    • Mandible (1)
• Cranial Bones:
  • Thin but remarkably strong for their weight

The Frontal Bone

• Forms the anterior portion of the cranium (forehead)
• Articulates posteriorly with parietal bones via the coronal suture
• Major markings include:
  • Supraorbital margins
  • Anterior cranial fossa
  • Frontal sinuses (internal and lateral to glabella).
• Development: Forms in two halves, usually fused by ages 5 or 6
• Some adults have a metopic suture
• Parts of the frontal bone:
  • Squamous part
  • Orbital part
  • Nasal part
• Supraorbital margin: Edge of the frontal part forming the superior border of the orbits
• Supraorbital foramen/notch: Opening or notch in the middle of the supraorbital margin
• Superciliary arches: Thickened ridges over the supraorbital margins supporting eyebrows
• Other features:
  • Frontal eminence
  • Glabella
  • Frontal sinus

The Occipital Bone

• Contributes to the posterior, lateral and inferior surfaces of the cranium
• Encircled by four parts: basilar, lateral (2), squamous
• Foramen magnum: large circular opening for cranial and spinal cavities connection
• Clivus(superior surface);slightly concave and sloped upwards in continuity with the sphenoid
• Pharyngeal tubercle (inferior surface), site for muscle and raphe attachment
• Other features
  • External occipital protuberance (inion)
  • Superior nuchal line
  • Occipital condyle
  • Hypoglossal canal

The Parietal Bones

• Contribute to the superior and lateral surface of the cranium.
• Connected by immovable joints called sutures.
• Major Sutures:
  • Lambdoid suture: Between occipital and parietal bones.
  • Sagittal suture: Between the parietal bones.
  • Coronal suture: Between the frontal and parietal bones.
  • Squamous suture: Between the parietal and temporal bones.

The Temporal Bones

• Form the inferolateral aspects of the skull
• The temporal bone is divided into four parts:
  • Squamous (flattened plate)
  • Tympanic (surrounds external acoustic meatus or ear canal)
  • Mastoid (posterior to the external acoustic meatus)
  • Petrous (dense portion housing middle and inner ear structures)
• Major Features of the temporal bone:
  • Zygomatic process:forms the zygomatic arch (cheek bone)
  • Mandibular fossa: Forms a joint with the condyle of the mandible
  • External acoustic meatus: Ear canal
  • Styloid process: Projects inferiorly from the tympanic part.
  • Mastoid process: Bony knob behind the earlobe.
  • Stylomastoid foramen: Located between mastoid and styloid processes, passage for facial nerve.
  • Mastoid foramen: Posterior to the mastoid process
  • Other features in Petrous Part:
    • Internal acoustic meatus
    • Carotid canal
    • Jugular foramen

The Sphenoid Bone

• Butterfly-shaped bone that spans the width of the middle cranial fossa
• Forms the central wedge that articulates with all other cranial bones.
• Consists of:
  • Body (median portion)
  • Two greater wings (lateral portion)
  • Two lesser wings (anterior portion)
  • Pterygoid processes (directed inferiorly)
• Other features:
  • Sella turcica: Bony enclosure for the pituitary gland.
  • Greater wings: Large, lateral wing-like processes that strengthen the sides of the skull; have openings(foramen rotundum, foramen ovale, and foramen spinosum)
  • Lesser wings: small wing-like processes anterior to the sella turcica
  • Superior orbital fissure: Irregular slit-like opening between lesser and greater wings.
  • Pterygoid processes: Plates that permit muscle attachment
  • Pterygoid canals
• Major Markings:
  • Sella turcica
  • Hypophyseal fossa
  • Pterygoid processes

The Ethmoid Bone

• Lies between the sphenoid and nasal bones.
• Forms most of the bony area between nasal cavity and orbits
• Composed of:
  • Cribriform plate: Perforated plate containing olfactory foramina
  • Crista galli: Raised ridge that projects upward
  • Perpendicular plate: Forms part of the nasal septum
  • Superior and middle nasal conchae: Bony projections that increase surface area for airflow.
  • Ethmoid sinuses: Air spaces within the bone

The Facial Bones

• The facial bones form the skeleton of the face.
• List of Facial Bones:
  • Nasal bones (2)
  • Lacrimal bones (2)
  • Zygomatic bones (2)
  • Maxillae (2)
  • Palatine bones (2)
  • Inferior nasal conchae (2)
  • Vomer (1)
  • Mandible (1)

The Mandible

• Largest and strongest bone of the face. Described as horseshoe shaped
• All muscles of mastication attach to the mandible
• Has different sections :
  • Body
  • Ramus
  • Head of the mandible
  • Neck of the mandible
  • Angle of the mandible
  • Coronoid process
  • Condylar process
  • Mandibular notch
  • Mental tubercle
  • Mental protuberance
  • Mental foramen
  • Alveolar process (supports mandibular teeth)
  • Parts of the Mandible:
    • Mylohyoid line
    • Mylohyoid groove
    • Sublingual fovea
    • Submandibular fovea
    • Mental spine
• The alveolar process supports the teeth
• Alveolar bone is resorbed when a tooth is lost

The Hyoid Bone

• Located at the C3 vertebral level, in front of the neck
• Unique as it does not articulate with any bone
• Attachment for hyoid muscles
• The upper and lower parts of the neck's hyoid muscles attach to this bone

This quiz covers key aspects of the occipital and frontal bones, including their anatomical features, functions, and relationships with other cranial structures. Test your knowledge on the important landmarks, sutures, and articulations of these cranial bones.