THE SPHENOID BONE. 27 



ination a body, two greater wings, two lesser wings, and 

 two pterygoid processes. When viewed from the front 

 it resembles a bat with wings extended. The body is 

 hollow, cuboidal in form, and presents superior, in- 

 ferior, anterior, and posterior surfaces. The greater and 

 lesser wings spring from the sides of the body. The 

 superior surface from before backward presents the fol- 

 lowing points : The ethmoidal spine for articulation with 

 the ethmoid ; this is a smooth surface of bone, slightly 

 grooved on each side of the median line for the accom- 

 modation of the olfactory tracts ; anteriorly, it forms a 



FIG. 11. SPHENOID BONE, UPPER SURFACE. 



spine which is received in an angle at the posterior por- 

 tion of the ethmoid. This surface is continuous laterally 

 with the upper surface of the lesser wings. Behind the 

 ethmoid spine is the optic groove, which lodges the optic 

 chiasm ; it terminates at each side at the optic foramen. 

 Behind the optic groove is the olivary body, an ovoidal 

 mass of bone which slightly overhangs a fossa posterior 

 to it, called the sella turcica, which lodges the pituitary 

 body. At the sides of this fossa, behind the olivary body, 

 are the middle clinoid processes, slight elevations which 

 give attachment to the dura mater. Overhanging the 



