Sphenoid bone

Borders 

The sphenoid bone has a common border with the frontal bone (via the sphenofrontal suture), the parietal bone (via the the sphenoparietal suture), the squamous part of the temporal bone (via the sphenosquamosal suture) and the occipital bone (via the spheno-occipital suture). As the sphenoid and occipital bone fuse during puberty ('tribasilar bone') the spheno-occipital suture disappears by the age of 25.

Main parts

There are four main parts to the sphenoid bone including:

• The body of the sphenoid bone;
• The lesser wings;
• The greater wings;
• The pterygoid processes.

Body

The body is the centrally positioned portion. Anteriorly, it contributes to the nasal cavity, laterally it builds the medial wall of the optic canal. Superiorly the body forms the sella turcica, the hypophyseal fossa and the dorsum sellae.

The sphenoidal sinuses are located in the sphenoid body behind the nasal cavity and divided by a septum. They contain the anterior and posterior clinoid processes respectively. The clivus slopes posterior to the body.

Lesser wings

The lesser wings arise superolaterally from the sphenoid body where they form the optic canal which contains the optic nerve, ophthalmic artery. The inferior surface participates in the lateral margin of the orbit while the superior surface forms part of the cranial cavity.

Greater wings

The greater wings arise posterolaterally from the body of the sphenoid bone.

Their lateral surfaces form the infratemporal surfaces. Their anterior surfaces make up part of the posterior aspect of the lateral wall of the orbit.

They contain three important openings near their roots:

• Foramen rotundum, traversed by the maxillary nerve. 
• Foramen ovale, which allows the passage of the mandibular nerve, accessory meningeal artery, lesser petrosal nerve and emissary vein.
• Foramen spinosum, traversed by the middle meningeal vessels and usually the spinous nerve, a branch of the mandibular nerve.

Between the body, lesser and greater wings is a large opening known as the superior orbital fissure where numerous nerves and vessels pass through. These vessels include the superior ophthalmic vein, ophthalmic nerve and its branches, abducent nerve, oculomotor nerve, trochlear nerve).

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Pterygoid processes

The pterygoid processes are extensions of the basal surface of the sphenoid body. Each process consists of a medial pterygoid plate and a lateral pterygoid plate. The lateral plate is wider and shorter than the medial and serves as the origin of the medial and lateral pterygoid muscles. At the inferior tip of the medial pterygoid plate is the small hook-shaped process, the pterygoid hamulus.

The processes contain two canals known as the pterygoid canal and palatovaginal canal. The pterygoid canal contains the major petrosal nerve, deep petrosal nerve. The palatovaginal (or pharyngeal) canal contains the pharyngeal nerve. 

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