B. Unpaired bones of the braincase

3. Sphenoid

The sphenoid is formed of two bones, the rostral presphenoid and the caudal basisphenoid. The sphenoid bones form the rostral base of the braincase. Passing through the sphenoid bone are the optic canal, orbital fissure, and alar canal in the caudal part of the orbit. The optic canal for the passage of the optic nerve and the orbital fissure for the passage of oculomotor, trochlear, abducent, and ophthalmic nerves.

The alar canal begins at the caudal alar foramen and ends at the rostral alar foramen. It provides a passage for the maxillary artery and nerve.