The sphenoid bone is the most complex bone of the human body. Because of its shape, it is also known as the "wasp bone". It makes up most of the middle part of the base of the skull and contributes to the floor of the middle cranial fossa of the skull.
The soft tissue structures such are the cranial nerves and parts of the brain are associated with this bone and have intense relations to it. The sphenoid bone also takes part into the forming of the many of the foramina and canals of the cranium.
|Structure||Body (median portion)
Two greater wings (lateral portion)
Two lesser wings (anterior portion)
Pterygoid processes (directed downwards)
Sphenofrontal suture with the frontal bone
Sphenoparietal suture with the parietal bone
Sphenosquamosal suture with the temporal bone
Spheno-ocipital suture with the occipital bone (disappears by the age 25 and the bones fuse together)
Body: anteriorly contributes to the nasal cavity; laterally - optic canal; superiorly - sella turcica, the hypophyseal fossa, dorsum sellae
Lesser wings: superolaterally - optic canal; inferiorly - lateral margin of the orbit; superiorly - cranial cavity; together with the body and greater wings builds the superior orbital fissure (superior ophthalmic vein; ophthalmic, abducent, oculomotor and trochlear nerves)
Greater wings: anteriorly - posterior aspect of the lateral orbital wall; contain foramen ovale (madibular nerve, accessory meningeal artery, lesser petrosal nerve, emissary vein) and foramen spinosum (middle meningeal vessels, meningeal branch of the mandibular nerve)
Pterygoid processes: contains pterygoid canal (major and deep petrosal nerves) and palatovaginal canal (pharyngeal nerve)
In this article you will find out all about the anatomy of the sphenoid bone, its parts, borders, and development.
There are four main parts to the sphenoid bone: the body (corpus), the lesser and greater wings (alae minores et majores) and the pterygoid processes.
The body is the most 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.
They contain the anterior and posterior clinoid processes respectively. The clivus slopes posterior to the body. The sphenoidal sinuses are located in the sphenoid body behind the nasal cavity and divided by a septum.
The lesser wings arise superolaterally from the sphenoid body where they form the optic canal (→ 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.
The greater wings arise posterolaterally from the body.
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 two important openings near their roots:
- foramen rotundum, which transmits the maxillary nerve
- foramen ovale, which allows the passage of the mandibular nerve, accessory meningeal artery, lesser petrosal nerve and emissary vein (mnemonic "MALE")
- foramen spinosum, that is traversed by the middle meningeal vessels, spinous nerve [branch of mandibular nerve]) lies at the posterior margin of the greater wings.
Between the body, lesser and greater wings is a large opening known as the superior orbital fissure where numerous nerves and vessels pass through (→ superior ophthalmic vein, ophthalmic nerve and its branches, abducent nerve, oculomotor nerve, trochlear nerve).
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The pterygoid processes are extensions of the basal surface of the sphenoid body. The processes contain two canals known as the pterygoid canal (→ major petrosal nerve, deep petrosal nerve, vessels of pterygoid canal) and the palatovaginal (or pharyngeal) canal (→pharyngeal nerve). A hamulus extends bilaterally from each medial pterygoid plate.
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.
The body and lesser wings of the sphenoid bone mature through classic endochondral ossification, whereas the pterygoid processes undergo intramembranous ossification.
The development of the greater wings of the sphenoid bone are exceptional since they are the only bony structures of the skull which go through both endochondral and intramembranous ossification.