SPHENOID BONE. 15 



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. 



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 outwards, terminate in a more or less acute 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 

 greater wing ; and is converted into a foramen by the articulation of this bone 

 with the frontal. It transmits the third, fourth, ophthalmic division of the fifth and 

 sixth nerves, and the ophthalmic vein. The anterior 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 (rtti^, a wing, fl8o<, likeness], one on each side (fig. 36), 

 descend perpendicularly from 

 the point where the body and 

 great wing unite. Each pro- 

 cess consists of an external 

 and an internal plate, separ- 

 ated behind by an interven- 

 ing 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 zygo- 

 matic fossa. It gives attach- 

 ment, by its outer surface, to 

 the External pterygoid; its 

 inner surface forms part of 

 the pterygoid fossa, and gives 

 attachment to the Internal 

 pterygoid. 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 depression, the scaphoid fossa, from which arises the 

 Tensor palati, and above which is seen the posterior orifice of the Vidian canal. 

 The outer surface of this plate forms part of the pterygoid fossa, the inner sur- 

 face forming the outer boundary of the posterior aperture of the nares. The 

 two pterygoid plates are separated below by an angular interval, in which the 

 pterygoid process, or tuberosity, of the palate bone is received. The anterior 

 surface of the pterygoid process is very broad at its base, and forms the pos- 



Fi &- 36. Sphenoid Bone. Posterior Surface. 



