Skull and Facial Bones

Skull Introduction & Neurocranium - Cranial Vault Chronicles

• Skull Divisions:
  • Neurocranium: Braincase; 8 bones.
  • Viscerocranium: Facial skeleton; forms face, orbits, nasal cavities, supports mastication.
• Neurocranial Bones:
  • Frontal (1): Forehead; supraorbital foramen.
  • Parietal (2): Sides/roof; temporal lines.
  • Temporal (2): Lateral walls/base; squamous, petrous, mastoid, tympanic parts. Foramina: carotid canal, IAM, jugular foramen (part).
  • Occipital (1): Posterior/base; foramen magnum, occipital condyles, EOP.
  • Sphenoid (1): "Keystone"; wings (greater/lesser), pterygoid processes. Foramina: optic canal, SOF, rotundum, ovale, spinosum.
  • Ethmoid (1): Anterior base; cribriform plate (olfactory foramina), crista galli.
• 📌 Mnemonic (Cranial Bones): "PEST OF" (Parietal, Ethmoid, Sphenoid, Temporal, Occipital, Frontal) - 6 types, 8 total.
• Sutures: Coronal, Sagittal, Lambdoid, Squamous.

⭐ Sphenoid: "keystone" of cranial floor; articulates with all other cranial bones.

Viscerocranium & Mandible - Facial Framework Facts

• Viscerocranium (Facial Skeleton): 14 bones. 📌 Mnemonic: "Virgil Can Not Make My Pet Zebra Laugh" (Vomer, Inferior Conchae, Nasal, Maxilla, Mandible, Palatine, Zygomatic, Lacrimal).
  • Maxillae (2): Upper jaw; infraorbital foramen; forms part of orbit, nasal cavity, hard palate. Site of Le Fort fractures.
  • Zygomatic (2): Cheekbones; forms zygomatic arch with temporal bone.
  • Nasal (2): Bridge of nose.
  • Lacrimal (2): Medial orbit wall; lacrimal fossa for lacrimal sac.
  • Palatine (2): Posterior hard palate; part of nasal cavity & orbit.
  • Inferior Nasal Conchae (2): Lateral walls of nasal cavity; scroll-like bones.
  • Vomer (1): Forms posterior/inferior part of nasal septum.
• Mandible (1): Lower jaw; largest, strongest facial bone.
  • Body: Mental foramen (mental nerve & vessels).
  • Ramus: Condylar process (articulates at TMJ), coronoid process (temporalis muscle attachment).
  • Mandibular foramen (inferior alveolar nerve & vessels).

⭐ The mental foramen, typically located inferior to the apex of the mandibular second premolar tooth, is a crucial landmark for administering mental nerve blocks for anesthesia of the lower lip and chin.

Skull Base, Foramina & Sutures - Cranial Communication Channels

• Cranial Fossae & Foramina:
  • Anterior Cranial Fossa: Frontal lobes.
    • Cribriform plate (CN I).
  • Middle Cranial Fossa: Temporal lobes.
    • Optic Canal (CN II, Ophthalmic a.)
    • Superior Orbital Fissure (CN III, IV, V1, VI, Ophthalmic v.)
    • Foramen Rotundum (CN V2)
    • Foramen Ovale (CN V3, Acc. meningeal a.) 📌 OVALE: Otic ganglion, V3, Accessory meningeal a., Lesser petrosal n., Emissary v.
    • Foramen Spinosum (Middle meningeal a. & v.)
  • Posterior Cranial Fossa: Cerebellum, brainstem.
    • Internal Acoustic Meatus (CN VII, VIII)
    • Jugular Foramen (CN IX, X, XI, IJV)
    • Hypoglossal Canal (CN XII)
    • Foramen Magnum (Medulla, Vertebral aa., CN XI spinal roots)

• Sutures & Fontanelles:
  • Sutures: Coronal, Sagittal, Lambdoid. Pterion (weakest point).
  • Fontanelles: Anterior (closes 18-24 months), Posterior (closes 2-3 months).

⭐ Pterion fracture (junction of 4 bones) can rupture the middle meningeal artery, causing epidural hematoma.

High‑Yield Points - ⚡ Biggest Takeaways

• Pterion: Weakest skull point; fracture risks middle meningeal artery injury.
• Cribriform plate (ethmoid): Transmits CN I; fracture can cause CSF rhinorrhea, anosmia.
• Foramen magnum: Transmits spinal cord, vertebral arteries, CN XI (spinal root).
• Sella turcica (sphenoid): Protects the pituitary gland.
• Le Fort fractures: Key midface fracture patterns; Le Fort I involves maxillary detachment.
• Mandible: Largest, strongest facial bone; forms temporomandibular joint (TMJ).
• Nasal septum: Key components are vomer and perpendicular plate of ethmoid.