THE SPHEXOID BONE. 



183 



boundary of the foramen lacerum medium, and presents the posterior aperture of 

 the Vidian canal for the passage of the Vidian nerve and artery. In front of the 

 spine the circumference of the great wing presents a serrated edge, bevelled at 

 the expense of the inner table below and of the external above, which articulates 

 with the squamous portion of the temporal bone. At the tip of the great wing a 

 triangular portion is seen, bevelled at the expense of the internal surface, for 

 articulation with the anterior inferior angle of the parietal bone. Internal to this 

 is a broad serrated surface, for articulation with the frontal bone: this surface is 

 continuous internally with the sharp inner edge of the orbital plate, which assists 

 in the formation of the sphenoidal fissure, and externally with the serrated margin 

 for articulation with the malar bone. 



The Lesser Wings (processes of Ingrassias) are two thin, triangular plates of 

 bone which arise from the upper and lateral parts of the body of the sphenoid, 

 and. projecting transversely outward, terminate in a sharp point (Fig. 143). The 

 superior surface of each is smooth, flat, broader internally than externally, and 

 supports part of the frontal lobe of the brain. The inferior surface forms the 

 back part of the roof of the orbit and the upper boundary of the sphenoidal fissure 

 or foramen lacerum anterius. This fissure is of a triangular form, and leads from 

 the cavity of the cranium into the orbit : it is bounded internally by the body of 

 the sphenoid above, by the lesser wing ; below, by the internal margin of the 

 orbital surface of the great wing and is converted into a foramen by the articu- 

 lation of this bone with the frontal. It transmits the third, the fourth, the three 

 branches of the ophthalmic division of the fifth, the sixth nerve, some filaments 

 from the cavernous plexus of the sympathetic, the orbital branch of the middle 

 meningeal artery, a recurrent branch from the lachrymal artery to the dura 

 mater, and the ophthalmic vein. The anterior border of the lesser wing is ser- 

 rated for articulation with the frontal bone ; the posterior, smooth and rounded, is 

 received into the fissure of Sylvius of the brain. The inner extremity of this 

 border forms the anterior elinoid process. The lesser wing is connected to the 

 side of the body by two roots, the upper thin and flat, the lower thicker, obliquely 

 directed, and presenting on its outer side, near its junction with the body, a small 

 tubercle, for the attachment of the common tendon of three of the muscles of the 

 eye. Between the two roots is the optic foramen, for the transmission of the optic 

 nerve and ophthalmic artery. 



The Pterygoid Processes (-TSO'J;. a wing : ?ooc, likeness), one on each side, 

 descend perpendicularly from the point where the body and greater wing unite 

 (Fig. 145). Each process c insists of an external and an internal plate, separated 

 behind by an intervening 

 notch the pteryyvid fossa ; 

 but joined partially in front. 

 The external pterygoid plate 

 is broad and thin, turned a 

 little outward, and forms 

 part of the inner wall of the 

 zyi. r '>matic fossa. It gives 

 attachment, b v its outer sur- 

 face, to the External ptery- 

 goid : its inner surface forms 

 part of the pterygoid f"- 

 and gives attachment to the 

 Internal pterygoid. The in- 

 ternal ptt- rag-rid plate is much 

 narrower and longer, curving 

 outward, at its extremity, 

 into a hook-like process of bone, the hamular process, around which turns the 

 tendon of the Tensor palati muscle. On the posterior surface of the base of this 

 plate is a small, oval, shallow depression, the scaphoid fossa, from which arises 



FIG. 145. Sphenoid bone. Posterior surface. 



