THE SPHENOID BONE. 45 



account of their development, were originally distinct. They are commonly united by earlier or 

 stronger anchylosis with the ethmoid or palate bones, so as to come away, at least in part, with 

 either of these in disarticulation of the skull, and thus lay open the sphenoidal sinuses. A small 

 portion of these bones sometimes appears on the inner wall of the orbit, between the ethmoid, 

 frontal, sphenoid, and palate bones (Cleland in Phil. Trans., 1862). 



Each lateral surface of the body is for the most part occupied by the attachments 

 of the two wings, but at the fore part, below the root of the small wing, there is a 

 small free surface which bounds the sphenoidal fissure internally and forms the hind- 

 most portion of the inner wall of the orbit (fig. 69, p. 66). 



The small or orbital wings extend nearly horizontally outwards on a level with 



GREAT WING 

 SMALL WING CEREBRAL SURF. 



HAMULAR PROC. SJBsSST 'PTERYCOIO NOTC 



PTERYGOID PROCESS 



Fig. 45. THE SPHENOID BONE, FROM BEHIND. (Drawn by D. Gunn.) 



the fore part of the superior surface of the body. The extremity of each is slender 

 and pointed, and comes very close to, but usually not into actual contact with, the 

 great wing. The superior surface forms part of the anterior fossa of the base of the 

 cranium ; the inferior overhangs the sphenoidal fissure and the back of the orbit. 

 The anterior border, thin and serrated, articulates with the orbital plate of the 

 frontal bone. The posterior border is prominent and free, and forms the boundary 

 between the anterior and middle cranial fossae, terminating internally in a smooth 

 rounded projection, the anterior clinoid process. Between the anterior clinoid pro- 

 cess and the olivary eminence is a semicircular notch in which the carotid groove 

 terminates ; and in front of this is the optic foramen perforating the base of the 

 wing. 



The great or temporal wings project outwards and upwards from the sides of 

 the body. The back part of each is placed horizontally, and occupies the angle 

 between the petrous and squamous portions of the temporal bone ; from its pointed 

 extremity it sends downwards a short and sharp projection, the spinous process. 

 The upper and fore part is vertical, and three-sided, lying between the cranial 

 cavity the orbit, and the temporal fossa (fig. 66, p. 64). The cerebral surface, of the 



