Cranial Bones: Sphenoid and Ethmoid

Sphenoid Bone

• Cranial bone forming part of the brain case.
• Located on the posterior orbits, forming part of the back wall of the eye socket.
• Lateral view of the skull shows the sphenoid.
• Best view is from inside the skull, revealing its full shape.
• Butterfly-shaped bone.

Key Parts of the Sphenoid Bone

• Optic Foramen:
  • Small, round hole in the sphenoid bone within the orbit.
  • The optic nerve passes through this foramen, transmitting visual input from the eye to the brain.
• Sella Turcica:
  • Depression in the medial part of the sphenoid bone.
  • Literally translates to "Turkish saddle."
  • Houses and protects the pituitary gland.
    • Pituitary gland regulates and controls the endocrine glands.
    • Endocrine system produces hormones.

Ethmoid Bone

• Deepest bone of the skull, mostly surrounded by other bones.
• Located in the orbit, forming the medial or inside wall.
• Forms portions within the nasal cavity.
• Partially visible within the cranial cavity.

Key Features of the Ethmoid Bone

• Cribriform Plate:
  • Two flattened areas of bone with numerous small holes.
  • "Criba" means "spaghetti strainer," indicating many little holes.
  • Olfactory Foramina:
    • Small holes within the cribriform plate.
    • Olfactory nerves pass through these holes, transmitting sensory input from the nasal cavity to the brain.
• Crista Galli:
  • Spike-like projection medial to the cribriform plate within the cranial cavity.
  • Translates to "rooster crest."
  • Serves as an anchor point for brain membranes.
  • Helps stabilize the brain within the skull, preventing it from slamming against the skull walls during sudden movements.