Presphenoid bone

The two parts that fuse early on in Men in order to form the sphenoid bone, stay separated much longer in the other Mammals. Usually they take more time to merge with each other than to the basilar basilar part of the occipital bone and especially to the ethmoid bone. Therefore they can be described as two different bones: the basisphanoid bone (Os basisphnoidale), -or posterior sphenoid- and the presphenoid bone (Os presphenoidale) -or anterior sphenoid. Each one of these parts has a body, median, and a pair of extensions raised dorsally, called wings. The presphenoid bone is always located a bit dorsally to the basisphenoid bone.

They are usually described together by french authors in order to avoid useless complications of the description. The resulting sphenoid bone has a body (Corpus) and two pairs of wings (Alae).

The body belongs mainly to the basisphenoid. It merges to the basilar part of the occipital bone and in front to the ethmoid bone.

Besides the wings that are raised dorsally, it has a strong ventral process on each side, the pterygoid process (Processus pterygoideus) that belongs to the basisphenoid bone.

The wings, two on each side, are temporal for one or basisphenoidal (Ala ossis basisphenoidalis), and orbital for the other or presphenoidal (Ala ossis presphenoidalis); they enter in the constitution of the lateral walls of the cranium.