152 



THE SKELETON. 



seen for the passage of arteries ; they are called the external orbital foramina. 

 Circumference of the great wing (Fig. 101) : commencing from behind, from the 

 body of the sphenoid to the spine, the outer half of this margin is serrated, for 

 articulation with the petrous portion of the temporal bone ; whilst the inner 

 half forms the anterior boundary of the foramen lacerum medium, and presents 

 the posterior aperture of the Yidian canal. In front of the spine the circum- 

 ference 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 trian- 

 gular portion is seen, bevelled at the expense of the internal surface, for arti- 

 culation 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. 



The Lesser Wings (processes of Ingrassias) (Fig. 101) are two thin triangular 

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

 sphenoid; and, projecting transversely outwards, terminate in a sharp point. 

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

 and supports the anterior 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 orbital 

 surface of the great wing and is converted into a foramen by the articulation 

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

 division of the fifth and the sixth nerves, and the ophthalmic vein. The ante- 

 rior border of the lesser wing is serrated 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 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 (ttilpvZ, a wing *Z5oj, likeness), (Fig. 103), one on each 

 side, descend perpendicularly from the point where the body and great wing 

 unite. Each process consists of an external and an internal plate, separated 



behind by an intervening 



Fig. 103. Sphenoid Bone. Posterior Surface. notch the pterygoid fossa ; 



but joined partially in front. 

 The external pterygoid plate 

 is broad and thin, turned a 

 little outwards, and forms 

 part of the inner wall of the 

 zygomatic fossa. It gives 

 attachment, by its outer sur- 

 face, to the External Ptery- 

 goid muscle; its inner sur- 

 face forms part of the ptery- 

 goid fossa, and gives attach- 

 ment to the Internal Ptery- 

 goid. The internal pterygoid 

 plate is much narrower and 

 longer, curving outwards, at 

 its extremity, into a hook- 

 like process of bone, the hamular process, around which turns the tendon of 

 the Tensor Palati muscle. At the base of this plate is a small, oval, shallow 



