sphenoid bone

An unpaired bone at the base of the skull, the sphenoid lies in front of the temporal bone and the basilar part of the occipital bone. Its outline has long been compared to a butterfly or a bat with its wings extended, and that comparison is preserved in the alternative name butterfly bone. The sphenoid is one of the seven bones that articulate to form the orbit, so it contributes to the walls of the eye socket as well as to the cranial floor. Its central position means it meets a large number of neighbouring cranial bones, and it is classified among the endochondral bones by its mode of ossification.