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The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the
sphenoid bone The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of occipital bone, basilar part of the occipital bone. The sphenoid bone is one of the seven bon ...
, positioned in the skull behind each eye. There is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward.


Structure

The greater wings of the sphenoid are two strong processes of bone, which arise from the sides of the body, and are curved upward, laterally, and backward; the posterior part of each projects as a triangular process that fits into the angle between the squamous and the petrous part of the
temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...
and presents at its apex a downward-directed process, the spine of sphenoid bone.


Cerebral surface

The superior or cerebral surface of each greater wing ig. 1forms part of the middle cranial fossa; it is deeply concave, and presents depressions for the convolutions of the
temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pr ...
of the brain. It has a number of foramina (holes) in it: * The foramen rotundum is a circular aperture at its anterior and medial part; it transmits the
maxillary nerve In neuroanatomy, the maxillary nerve (V) is one of the three branches or divisions of the trigeminal nerve, the fifth (CN V) cranial nerve. It comprises the principal functions of Sense, sensation from the maxilla, nasal cavity, Sinus (anatomy ...
. * The foramen ovale is behind and lateral to this; it transmits the
mandibular nerve In neuroanatomy, the mandibular nerve (V) is the largest of the three divisions of the trigeminal nerve, the fifth Cranial nerves, cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which ...
, the
accessory meningeal artery Accessory may refer to: * Accessory (legal term), a person who assists a criminal In anatomy * Accessory bone * Accessory breast * Accessory kidney * Accessory muscle * Accessory nucleus, in anatomy, a cranial nerve nucleus * Accessory nerve * ...
, and sometimes the lesser petrosal nerve. * The sphenoidal emissary foramen is occasionally present; it is a small aperture medial to the foramen ovale, opposite the root of the pterygoid process; it opens below near the scaphoid fossa, and transmits a small vein from the cavernous sinus. * The foramen spinosum, in the posterior angle near to and in front of the spine; it is a short canal that transmits the middle meningeal vessels and a recurrent branch from the
mandibular nerve In neuroanatomy, the mandibular nerve (V) is the largest of the three divisions of the trigeminal nerve, the fifth Cranial nerves, cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which ...
. * The foramen petrosum, a small occasional opening, between the foramen spinosum and foramen ovale, for transmission of the lesser petrosal nerve.


Lateral surface

The lateral surface ig. 2is convex, and divided by a transverse ridge, the infratemporal crest, into two portions. * The superior temporal surface, convex from above downward, concave from before backward, forms a part of the temporal fossa, and gives attachment to the temporalis; * the inferior infratemporal surface, smaller in size and concave, enters into the formation of the infratemporal fossa, and, together with the infratemporal crest, serves as an attachment to the lateral pterygoid muscle. It is pierced by the foramen ovale and foramen spinosum, and at its posterior part is the sphenoidal spine, which is frequently grooved on its medial surface for the chorda tympani nerve. To the sphenoidal spine are attached the sphenomandibular ligament and the tensor veli palatini muscle. Medial to the anterior extremity of the infratemporal crest is a triangular process that serves to increase the attachment of the lateral pterygoid muscle; extending downward and medialward from this process on to the front part of the lateral pterygoid plate is a ridge that forms the anterior limit of the infratemporal surface, and, in the articulated skull, the posterior boundary of the pterygomaxillary fissure.


Orbital surface

The orbital surface of the great wing ig. 2 smooth, and quadrilateral in shape, is directed forward and medially and forms the posterior part of the lateral wall of the orbit. * Its upper serrated edge articulates with the orbital plate of the frontal bone. * Its inferior rounded border forms the postero-lateral boundary of the inferior orbital fissure. * Its medial sharp margin forms the lower boundary of the superior orbital fissure and has projecting from about its center a little tubercle that gives attachment to the inferior head of the lateral rectus muscle; at the upper part of this margin is a notch for the transmission of a recurrent branch of the lacrimal artery. * Its lateral margin is serrated and articulates with the zygomatic bone. * Below the medial end of the superior orbital fissure is a grooved surface, which forms the posterior wall of the pterygopalatine fossa, and is pierced by the foramen rotundum.


Margin

Commencing from behind ig. 2 that portion of the circumference of the great wing that extends from the body to the spine is irregular. * Its ''medial half'' forms the anterior boundary of the foramen lacerum, and presents the posterior aperture of the pterygoid canal for the passage of the corresponding nerve and artery. * Its ''lateral half'' articulates, by means of a synchondrosis, with the petrous portion of the temporal, and between the two bones on the under surface of the skull, is a furrow, the sulcus of the auditory tube, for the lodgement of the cartilaginous part of the
auditory tube The Eustachian tube (), also called the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear, of which it is also a part. In adult humans, the Eustachian tube is approximately long and in diameter. It ...
. In front of the spine the circumference presents a concave, serrated edge, bevelled at the expense of the inner table below, and of the outer table above, for articulation with the squamous part of the
temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...
. At the tip of the great wing is a triangular portion, bevelled at the expense of the internal surface, for articulation with the sphenoidal angle of the
parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...
; this region is named the pterion. Medial to this is a triangular, serrated surface, for articulation with the frontal bone; this surface is continuous medially with the sharp edge that forms the lower boundary of the superior orbital fissure, and laterally with the serrated margin for articulation with the zygomatic bone.


Development

The greater wing of the sphenoid bone starts as a separate bone, and is still separate at birth in humans.


Function

The
sphenoid bone The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of occipital bone, basilar part of the occipital bone. The sphenoid bone is one of the seven bon ...
assists with the formation of the base and the sides of the skull, and the floors and walls of the orbits. It is the site of attachment for most of the muscles of mastication. Many foramina and fissures are located in the sphenoid that carry nerves and blood vessels of the head and neck, such as the superior orbital fissure (with ophthalmic nerve), foramen rotundum (with
maxillary nerve In neuroanatomy, the maxillary nerve (V) is one of the three branches or divisions of the trigeminal nerve, the fifth (CN V) cranial nerve. It comprises the principal functions of Sense, sensation from the maxilla, nasal cavity, Sinus (anatomy ...
) and foramen ovale (with
mandibular nerve In neuroanatomy, the mandibular nerve (V) is the largest of the three divisions of the trigeminal nerve, the fifth Cranial nerves, cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which ...
).


Clinical significance

In patients with neurofibromatosis type 1, malformation of the sphenoid bone wings may occur, due to aberrant cell development. This can ultimately lead to blindness if left untreated.


In other animals

In many mammals, e.g. the dog, the greater wing of the sphenoid bone stays through life a separate bone called the alisphenoid.


Additional images

File:Orbital_bones.png, The seven bones that articulate to form the orbit. File:Gray187.png, Base of skull. Inferior surface. File:Gray189.png, Left infratemporal fossa. File:Gray190.png, The skull from the front. File:Gray310.png, Articulation of the mandible. Medial aspect. File:Gray889.png, Muscles of the right orbit. File:Slide24hhhh.JPG, Greater wing of sphenoid bone File:Slide8jjjj.JPG, Greater wing of sphenoid bone File:Slide1mmmm.JPG, Greater wing of sphenoid bone File:Slide7nnnn.JPG, Greater wing of sphenoid bone File:Slide3pppp.JPG, Greater wing of sphenoid bone


External links

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References

{{Authority control Bones of the head and neck