sphenoid

The sphenoid is a single, central bone at the base of the skull. It is unpaired and serves as a keystone of the skull because it articulates with multiple other cranial bones. It contributes to the floor of the middle cranial fossa, the posterior portion of the orbit, and the roof of the nasal cavity, and it houses important neurovascular structures.

Anatomically, the sphenoid consists of a central body, two pairs of wings (greater and lesser), and two pterygoid processes that project downward. The body contains the sphenoidal sinuses. The lesser wings form part of the anterior skull base and the roof of the optic canal, while the greater wings contribute to the floor of the middle cranial fossa and the lateral wall of the orbit. The pterygoid processes have medial and lateral plates that serve as attachment points for the pterygoid muscles. Several foramina and canals traverse the bone: the optic canal transmits the optic nerve and ophthalmic artery; the superior orbital fissure transmits CN III, IV, V1, and VI and sympathetic fibers; the foramen rotundum transmits CN V2; the foramen ovale transmits CN V3; the foramen spinosum transmits the middle meningeal vessels and meningeal nerves; and the foramen lacerum is largely filled with cartilage in life.

The sphenoid articulates with all other cranial bones except the mandible. Its sella turcica—a saddle-shaped enclosure on the body—houses the pituitary gland, with the tuberculum sellae anteriorly, the hypophysial fossa in the center, and the dorsum sellae posteriorly. Clinically, the bone is relevant in sphenoid sinusitis and skull base fractures and is key to skull anatomy due to its central position.