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Portrait of Sphenoid bone

Anatomy · Bones

Sphenoid bone

The keystone of the skull

Skull · cranium

The sphenoid is a single, butterfly-shaped bone in the middle of the skull base, behind the eyes. It has a hollow central body, two pairs of wings and two downward pterygoid processes, and it touches almost every other bone of the skull. It holds the pituitary gland in its saddle-shaped sella turcica.

How to spot them

  • ▸A single wedge or butterfly-shaped bone at the centre of the skull base, seen from above as a bat-like shape
  • ▸Central body with a saddle-shaped hollow, the sella turcica, that holds the pituitary gland
  • ▸Lesser and greater wings; between them the superior orbital fissure leads into the orbit
  • ▸Contains an air sinus in its body, the most posterior of the paranasal sinuses

What to know

The butterfly-shaped keystone bone that articulates with almost every other bone of the skull

Sphenoid bone — the OpenStax 'keystone' bone.

The saddle-shaped depression on its upper surface, named for the Ottoman horse saddle, cradles the pituitary gland

Sphenoid bone — the sella turcica ('Turkish saddle') and hypophyseal fossa.

Surgeons reach the pituitary through this bone and its sinus, entering by the nose in endoscopic surgery

Sphenoid bone — endoscopic trans-sphenoidal surgery.

Its lesser wing has a canal through which the optic nerve and ophthalmic artery reach the eye

Sphenoid bone — the optic canal, with the superior orbital fissure between lesser and greater wings.

Three foramina in its greater wing transmit the maxillary nerve, the mandibular nerve and the middle meningeal vessels

Sphenoid bone — foramina rotundum, ovale and spinosum.

Two plates descending from it behind the nose give origin to the medial and lateral pterygoid muscles

Sphenoid bone — the medial and lateral pterygoid plates.

Its name comes from the Greek for wedge-shaped

Sphenoid bone — sphenoeides, wedge-like.

Key ideas

  • Body, greater wings, lesser wings and pterygoid processes: the greater wing forms part of the floor of the middle cranial fossa, the side of the skull and the back wall of the orbit.
  • The lesser wings separate the anterior from the middle cranial fossa.

Quick-fire facts

  • •Articulates with twelve other bones: occipital, vomer, ethmoid, frontal (unpaired), temporal, parietal, zygomatic and palatine (paired)
  • •The pterion is where the sphenoid greater wing meets the frontal, parietal and temporal bones
  • •Sella turcica: tuberculum sellae in front, hypophyseal fossa in the floor, dorsum sellae behind
  • •Anterior clinoid processes arise from the lesser wings and posterior clinoid processes from the dorsum sellae; the tentorium cerebelli attaches to them
  • •The optic chiasm lies in a shallow groove, the chiasmatic groove, in front of the sella turcica
  • •The sphenoid sinus lies in the body just below the sella turcica
  • •The two sphenoidal sinuses are separated by a septum and open into the nasal cavity, so the body of the bone is essentially hollow
  • •The pterygoid processes descend where the body meets the greater wing

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Sources