The sphenoid bone is one of the most complex bones of the human body. Due to its shape, it is also referred to 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 main function of the sphenoid bone is to provide the foramina and canals for the passage of neurovascular structures to and from the cranium.
In this article you will find out all about the anatomy of the sphenoid bone, its parts, borders, and development.
|Structure||Body (median portion)
Two greater wings (lateral portion)
Two lesser wings (anterior portion)
Pterygoid processes (directed inferiorly)
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: contain pterygoid canal (major and deep petrosal nerves) and palatovaginal canal (pharyngeal nerve)
- Osseous development
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.
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.
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.
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.
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 two 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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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.
Test your knowledge on the sphenoid bone with this quiz.
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.
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