252 MAMMALIAN ANATOMY 



process. The transverse posterior margin is slightly emarginate and 

 joins the upper anterior margin of the basisphenoid. 



The narrow anterior part of the superior surface, included between 

 the nearly straight parts of the anterior lateral borders, is gently con- 

 cave from side to side and faces slightly forward as well as upward. 

 It forms a floor for the olfactory fossa, and a support for the olfac- 

 tory lobes of the brain. The lower part of the falx cerebri, the 

 membranous partition which divides these lobes, is attached along the 

 middle line. The part of the superior surface lying between the 

 lateral angles, in front of the optic foramina, faces upward and back- 

 ward, and is faintly convex from before backward and slopes inward 

 and downward on each side to the middle line. The part of the wing 

 lying outside of the foramen is slightly grooved transversely. The 

 narrow part lying between the optic foramina is the transverse optic 

 groove ; it is sometimes sharply separated from the anterior portion 

 by the continuation inward of a ridge from the anterior margins of 

 the optic foramen. It faces backward at a still greater angle. It is 

 smooth and convex from side to side. Its outer margins are rounded, 

 and it passes gently into the orbital surface. The surface behind the 

 optic groove is known as the olivary eminence. It faces almost 

 directly upward, and is slightly convex from before backward. Its 

 sides are prolonged forward and outward as the rounded posterior 

 roots of the small wings or orbitosphenoids, and close the optic 

 foramina behind. Its posterior angles are the anterior clinoid l pro- 

 cesses. 



Each lateral or orbital surface (Figs. 183, 185) is about twice as 

 long as it is high. It is somewhat higher over the optic foramen and 

 lower at the posterior end. Its lower margin is almost straight, and is 

 serrated ; it articulates with the vertical plate of the palatine for the 

 anterior half and with the alisphenoid for the posterior half. The 

 vertical anterior margin is irregularly arcuate, and joins the posterior 

 border of the ethmoidal part of the vertical plate of the palatine. The 

 superior border slopes from the front gradually up to the tip of the small 

 wing, and then slopes abruptly downward and backward to the posterior 

 margin. It is serrated, and sometimes bevelled at the expense of the 

 surface throughout its course, except in the small posterior part which 

 forms the margin of the sphenoidal fissure. From the front to the tip 



1 From (dr.) dine, a bed, and eides, like. 



