OS SPHENOIDES. 



83 



Laterally, the body of the sphenoides is extended into the 

 portions called the great ivings or temporal processes. These 

 great icings compose the largest part of the bone, and their 

 internal surface forms a portion of the middle fossa of the base 

 of the cranium. Externally, the surface of each great wing is 

 divided into two portions : one of which is lateral, and unites 

 to the frontal, temporal, and malar bones, forming part of the 

 smooth surface for the temporal muscle ; the other portion 

 forms part of the orbit of the eye,' and is very regular and 

 smooth. As the ethmoid bone forms part of the inside, this 

 portion of the great wing forms part of the outside of the orbit, 

 and is termed the orhitary process of the sphenoid bone. The 

 horizontal part of each wing terminates in an acute angle 

 termed spinous process, which penetrates between the petrous 

 portion and the articulating cavity of the temporal bone. In 

 this angle is the foramen for the principal artery of the dura 

 mater ; near the point of the angle is a small process, which 

 projects from the basis of the cranium, and is called styloid. 



Fig. 19.* • The pterygoid pro- 



cesses pass downwards in 

 a direction almost per- 

 pendicular to the base of 

 the skull. Each of them 

 has two plates, and a 

 middle fossa facing back- 

 wards ; to complete the 

 comparison, they should 

 be likened to the legs of the bat, but are inaccurately named 

 pterygoid, or wing-like processes. The external plates 

 are broadest, and the internal are longest. From each side of 



* The antero-infciior view of the sphenoid bone. 1. The .elhmoid spine. 

 2. The rostrum. 3. The sphenoidal spongy bone, partly closing the left opening 

 of the sphenoidal cells. 4. The lesser wing. 5. The Ibramen opticum piercing 

 the base of the lesser wing. 6. The sphenoidal fissure. 7. The foramen rotun- 

 dum. 8. The orbital surface of the greater wing. 9. Its temporal surface. 10. 

 The pterygoid ridge. 11. The pterygo-palaiine canal. 12. The foramen of 

 entrance to the Vindian canal. 13. The internal pterygoid plate. 14. The 

 hamular process. 15. The external pterygoid jilale. 16. The foramen spino- 

 sum. 17. The foramen ovale. 18. The extremity of the spinous process of 

 the sphenoid. 



