THE SKULL THE CRANIUM 



251 



above are turned outward and prolonged upward as pointed wings. 

 At the base of each wing is a large optic foramen. 



The anterior sphenoid presents a superior, an inferior, an anterior, 

 a posterior surface, and two lateral surfaces. 



The superior surface (Fig. 182) has the outline of an irregular 

 hexagon, whereof the anterior and posterior sides are transverse, the 



Presphenoid, with Vomer 



FIG. 182. 



Ethmoidal Crest, with Mesethmoid. 



Entrance to Sphenoidal Sinus. 



Orbitosphenoid, with Frontal. 



With Alisphenoid. | \J*^ ~~_^ Optic Foramen - 

 With Hasisphenoid. 



PRESPHENOID AND ORBITOSPHENOIDS, INNER OR UPPER SURFACE. 



long anterior lateral sides are directed backward and outward, and the 

 shorter posterior lateral sides forward and outward. A line drawn 

 between the acute lateral angles thus formed would divide the bone 

 into a posterior third and an anterior two-thirds. The anterior margin 

 is deeply emarginate on each side of the middle line, to articulate 

 with the lower ends of the cribriform plate of the ethmoid. The 

 median, forward prolongation is the ethmoidal spine, and is the 

 upper border of the ethmoidal crest. Each anterior lateral border is 

 ernargmate, the concavity facing outward and forward ; it is jagged, 

 encroaching to a greater or less degree on the superior surface above 

 and on the inferior surface behind, and articulates with part of the 

 lower border of the frontal. The posterior lateral margins are thin and 

 measurably straight ; they form also the posterior margins of the wings. 

 Each margin in its outer two-thirds or more is serrate, and articulates 



O 



with the front border of the alisphenoid (Fig. 181) ; in its inner 

 third or less it is free as the inner part of the upper margin of the 

 sphenoidal fissure, and gives attachment to the dura of the brain. Its 

 posterior angle is more or less prolonged into the anterior clinoid 



