Overview
This lecture covers the major bones, sutures, and surface landmarks of the skull from different anatomical perspectives, and introduces the cranial fossae, including their clinical relevance and key foramina.
Anterior Skull: Bones, Sutures & Landmarks
- The frontal bone forms the forehead above the eyebrows.
- The zygomatic bone shapes the cheeks; maxilla forms the upper jaw and lateral nose.
- The nasal bone makes the bridge of the nose; mandible is the lower jaw.
- The coronal suture separates the frontal and parietal bones.
- The frontal sinus is a mucosa-lined cavity within the frontal bone.
- Supraorbital margin is the superior rim of the orbit under the eyebrow.
- Supraorbital notch/foramen transmits the supraorbital nerve and artery.
- Optic canal contains cranial nerve II (optic nerve) and ophthalmic artery.
- Superior orbital fissure transmits ophthalmic vein, cranial nerves III, IV, V1, and VI.
- Inferior orbital fissure transmits the infraorbital nerve, artery, and inferior ophthalmic vein.
- Nasolacrimal duct drains tears from the orbit to the nasal cavity.
- Infraorbital foramen, mental foramen, and supraorbital foramen transmit V2, V3, and V1 branches, respectively, for sensory innervation.
Lateral Skull: Bones, Sutures & Landmarks
- Parietal bone forms the lateral wall; temporal bone above ears; sphenoid behind the orbit.
- The zygomatic arch is formed by zygomatic and temporal bones, attachment for masseter muscle.
- Mandible components: ramus (vertical part), coronoid process (muscle attachment), mandibular condyle (TMJ).
- Coronal suture (frontal/parietal), squamous suture (parietal/temporal), lambdoid suture (parietal/occipital).
- The pterion is a thin region where frontal, parietal, temporal, and sphenoid bones meet.
- The middle meningeal artery runs deep to the pterion; injury can lead to epidural hematoma.
- Mastoid process (breast-shaped, behind ear) contains air cells.
- External acoustic meatus is the ear canal entry.
- Petrous part of temporal bone houses internal ear structures.
Posterior & Superior Skull: Bones, Sutures & Landmarks
- Occipital bone forms the back of the skull; parietal bones on the sides.
- Lambdoid suture between occipital and parietal bones; sagittal suture between parietal bones.
- External occipital protuberance and superior/inferior nuchal lines are attachment sites for neck muscles.
- Occipital condyles articulate with C1 vertebra for head nodding.
Cranial Fossae & Internal Skull Base
- Anterior cranial fossa: frontal and ethmoid bones; houses cribriform plate for olfactory nerves.
- Middle cranial fossa: sphenoid and temporal bones; features sella turcica (pituitary fossa).
- Posterior cranial fossa: mostly occipital bone; supports cerebellum and brainstem.
- Key foramina: optic canal (CN II), superior orbital fissure (CN III, IV, V1, VI), foramen rotundum (V2), foramen ovale (V3), foramen spinosum (middle meningeal artery), foramen magnum (spinal cord, vertebral arteries, CN XI), jugular foramen (internal jugular vein, CN IX, X, XI).
Inferior Skull Base: Bones & Landmarks
- Maxilla and palatine bones form the hard palate; vomer forms part of nasal septum.
- Pterygoid processes (medial/lateral plates) of sphenoid serve muscle attachments.
- Mandibular fossa in temporal bone articulates with mandible for TMJ.
- Carotid canal transmits the internal carotid artery; stylomastoid foramen transmits facial nerve.
Cranial Fossae Overview
- Three cranial fossae: anterior, middle, posterior; stepwise depressions in the skull base.
Key Terms & Definitions
- Suture — a fibrous joint connecting skull bones.
- Foramen — a hole allowing passage for nerves/vessels.
- Cranial fossa — depression in the skull base housing brain regions.
- Pterion — region where four skull bones meet, clinically vulnerable.
- Sella turcica — saddle-shaped depression in sphenoid for the pituitary gland.
Action Items / Next Steps
- Review skull bone diagrams for bone and foramen locations.
- Practice naming and identifying cranial nerves passing through each foramen.
- Memorize key sutures and clinical implications, especially the pterion.