254 



MAMMALIAN ANATOMY 



of the wing it articulates with the posterior part of the lower edge of 

 the orbital plate of the frontal ; behind this point, with the anterior 

 edge of the alisphenoid. The posterior margin is short and directed 

 downward and forward. A. line, more or less prominent, which rises 

 from the lower border, jnst behind the optic foramen, and, running ob- 

 liquely forward, ends near the middle of the anterior margin, divides 

 the lateral surface into an upper and a lower part. The lower part 

 is concave from above downward, and in some specimens, owing to its 

 narrowness, becomes a shallow groove ; it is also concave from before 

 backward. It ends behind at the groove for the sphenoidal fissure and 

 gives origin to fibres of the external pterygoid muscle. The region 

 above this line is concave from before backward for the anterior half, 

 and slightly concave from above downward. It then begins to slope 

 outward, becomes the under surface of the wing, and faces downward, 

 forward, and outward. At its posterior part, underneath and behind 

 the optic foramen, the lateral surface turns inward, and, facing outward 

 and backward, becomes a groove running downward, backward, and 

 inward which forms the inner Avail of the sphenoidal fissure. 



On the inferior or external surface (Fig. 184) of the presphenoid, 

 in the middle line, is a smooth median ridge, the only part of the bone 



FIG. 184. 



With Vomer. 



With Palatine 



With Ptfrygoid 



Orbitosphenoid, with Frontal. 



Optic Foramen. 



With Alisphenoid. 

 Presphenoid, with Basisphenoid. 



PRESPHENOID AND ORBITOSPHENOIDS, OUTER OR LOWER SURFACE. 



rming u-ith 

 the Sphenoidal Fissure. 



which shows on the outside or base of the skull. It is rounded, and 

 varies in width, but almost always presents a middle, flatter and wider 

 part. On each side of this ridge, and between it and the lateral 

 margins, is a rough articular surface, whereof all in front of the 



