| Greater wing of sphenoid bone | |
| Latin: | ala major ossis sphenoidalis |
| Width: | 300 |
The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone, 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.
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 and presents at its apex a downward-directed process, the spine of sphenoid bone.
The superior or cerebral surface of each greater wing [Fig. 1] forms part of the middle cranial fossa; it is deeply concave, and presents depressions for the convolutions of the temporal lobe of the brain. It has a number of foramina (holes) in it:
The lateral surface [Fig. 2] is convex, and divided by a transverse ridge, the infratemporal crest, into two portions.
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.
The orbital surface of the great wing [Fig. 2], smooth, and quadrilateral in shape, is directed forward and medially and forms the posterior part of the lateral wall of the orbit.
Commencing from behind [Fig. 2], that portion of the circumference of the great wing that extends from the body to the spine is irregular.
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.
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; 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.
The greater wing of the sphenoid bone starts as a separate bone, and is still separate at birth in humans.
The sphenoid bone 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) and foramen ovale (with mandibular nerve).[1]
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 many mammals, e.g. the dog, the greater wing of the sphenoid bone stays through life a separate bone called the alisphenoid.