Skull Bones, Markings, and Associated Structures

Cranial Bones

  • Frontal Bone (1): Forms forehead and roof of eye sockets.
  • Parietal Bones (2): Form sides and roof of cranium.
  • Temporal Bones (2): Sides of the head, near ears.
    • External Acoustic Meatus: Opening for ear canal.
    • Zygomatic Process: Forms part of the zygomatic arch.
    • Mandibular Fossa: Depression on temporal bone for mandibular condyle, forming the temporomandibular joint (TMJ).
    • Mastoid Process: Rounded projection for neck muscle attachment.
    • Styloid Process: Slender projection for ligament attachment (hyoid bone support) and muscles of tongue/pharynx.
  • Occipital Bone (1): Forms back of the skull.
    • Foramen Magnum: Large hole for the spinal cord and brainstem connection.
    • Occipital Condyles: Rounded projections on either side of the foramen magnum, articulate with the first vertebra (C_1) for "yes" head motion.
  • Sphenoid Bone (1): Keystone of the cranium, found on the cranial floor. Articulates with all other cranial bones.
    • Sella Turcica: Saddle-shaped depression housing the pituitary gland.
    • Optic Foramen (Canal): Holes for optic nerves to pass.
  • Ethmoid Bone (1): Supports part of the nasal cavity, difficult to see from exterior.
    • Cribriform Plate: Superior portion with olfactory foramina.
    • Olfactory Foramina: Small holes in cribriform plate for olfactory nerves (smell).
    • Perpendicular Plate: Forms the superior portion of the bony nasal septum.
    • Crista Galli: Superior projection, serves as an attachment for brain dura mater.

Facial Bones

  • Nasal Bones (2): Form the bridge of the nose.
  • Maxillae (2): Upper jawbone; articulates with all facial bones except the mandible.
    • Palatine Processes: Form the anterior portion of the hard palate.
  • Palatine Bones (2): Form the posterior portion of the hard palate and a small part of the eye socket.
    • Cleft Palate: Occurs if palatine processes or palatine bones do not fuse during development.
  • Zygomatic Bones (2): Cheekbones, form part of the eye socket.
    • Temporal Process: Component of the zygomatic arch (fuses with the zygomatic process of temporal bone).
  • Lacrimal Bones (2): Smallest facial bones, within the eye socket.
    • Lacrimal Fossa: Hole for tear drainage into the nasal cavity.
  • Inferior Nasal Conchae (2): Scroll-like bones in the nasal cavity, lined with mucous membrane to slow, filter, warm, and humidify inhaled air.
  • Vomer Bone (1): Forms the inferior portion of the bony nasal septum.
  • Mandible (1): Lower jawbone, largest and strongest facial bone; the only movable skull bone.
    • Condylar Process (Mandibular Condyle): Articulates with the mandibular fossa of the temporal bone to form the TMJ.
    • Coronoid Process: Shark fin-shaped projection for temporalis muscle attachment.

Eye Orbit (7 Bones)

  • Cranial Bones (3): Frontal, Sphenoid, Ethmoid.
  • Facial Bones (4): Palatine, Zygomatic, Lacrimal, Maxilla.
  • Mnemonic: Make Larry Eat Spinach (Maxilla, Lacrimal, Ethmoid, Sphenoid).

Nasal Septum (Bony)

  • Superior Portion: Perpendicular plate of the ethmoid bone.
  • Inferior Portion: Vomer bone.

Paranasal Sinuses

  • Location: Air-filled chambers within the Frontal, Sphenoid, Ethmoid, and Maxillary bones.
  • Functions:
    • Lighten the skull.
    • Warm, humidify, and purify inhaled air.
    • Serve as resonating chambers for voice production.
  • Sinusitis: Inflammation of the mucous membrane lining the sinuses, often due to blockage or infection, causing pressure/pain.

Sutures

  • Definition: Immovable joints between cranial bones.
  • Coronal Suture: Unites frontal bone with the two parietal bones.
  • Sagittal Suture: Unites the two parietal bones.
  • Lambdoid Suture: Unites the two parietal bones with the occipital bone.
  • Squamous Suture: Unites a parietal bone with a temporal bone.

Fontanels (Soft Spots)

  • Definition: Areas of unossified fibrous connective tissue in fetal and infant skulls.
  • Purpose:
    • Allow skull flexibility during vaginal birth.
    • Accommodate rapid brain growth during the first two years of life.
  • Ossification: Typically replaced by bone (forming sutures) by approximately two years of age.

Hyoid Bone (1)

  • Location: Suspended midair between the mandible and larynx by ligaments; does not articulate with any other bone.
  • Functions:
    • Supports the tongue.
    • Helps keep the larynx (voice box) open.
    • Serves as an attachment point for muscles of the tongue, larynx, and pharynx.
  • Forensic Significance: Frequent fracture site in strangulation cases.