THE SPHENOID BONE. 75 



I above by a serrated edge, for articulation with the frontal bone; below, by a 

 rounded border which enters into the formation of the spheno-maxillary fissure. 

 Internally, it presents a sharp border, which forms the lower boundary of the 

 sphenoidal fissure, and has projecting from about its centre a little tubercle of 

 bone, which gives origin to one head of the External rectus muscle of the eye; 

 and at its upper part is a notch for the transmission of a recurrent branch of the 

 lachrymal artery: externally it presents a serrated margin for articulation with 

 the malar bone. One or two small foramina may occasionally be seen for the 

 passage of branches of the deep temporal arteries; they are called the external 

 orbital foramina. Circumference of the great wing (Fig. 37), commencing from 

 behind, that portion of the circumference from the body of the sphenoid to the 

 spine, is serrated and articulates by its outer half with the petrous portion of the 

 temporal bone, while the inner half forms the anterior 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 por- 

 tion 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 triangular, 

 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 for- 

 mation 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. 37). 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 clinoid 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 origin 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 (Trre^uf , a wing ; slooc, likeness), one on each side, 

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

 (Fig. 39). Each process consists of an external and an internal plate, which 

 are joined together by their anterior borders above, but are separated below, 

 leaving an angular cleft, the pterygoid notch, in which the pterygoid process or 

 tuberosity of the palate bone is received. The two plates diverge from each 

 other from their line of connection in front, so as to form a V-shaped fossa, the 

 pterygoid fossa. The external pterygoid plate is broad and thin, turned a little 

 outward, and, by its outer surface, forms part of the inner wall of the zygomatic 

 fossa, giving attachment to the External pterygoid; its inner surface forms part 



