THE SPHENOID BONE. 41 



backwards, making a smooth rounded knob, the anterior clinoid process, 

 which inclines towards the posterior process of the same name, and is 

 grooved on its inner margin for the internal carotid artery. 



The PTERYGOID PROCESSES project downwards and slightly forwards, 

 between the body and the great wings. Each consists of two plates united 

 in front and diverging behind, so as to enclose between them the pterygoid 

 fossa. The external pterygoid plate lies in a plane extending backwards and 

 outwards ; its outer surface bounds the zygomatic fossa, and gives attach- 

 ment to the external pterygoid muscle. The internal pterygoid plate is 

 longer and narrower than the external, and is prolonged into a slender 

 process turned outwards and named the hook-like or hamular process, round 

 which in a groove plays the tendon of the tensor palati muscle. At its base, 

 the internal plate turns inwards beneath the body, from which its extremity 

 remains distinct as a slightly raised edge, which articulates with the margin 

 of the vomer ; and externally to this it is marked by a small groove, which 

 contributes with the palate bone to form the pterygo-palatine canal. The 

 walls of the pterygoid fossa are incomplete at the lower part in the dis- 

 articulated sphenoid bone, an angular interstice existing between the plates, 

 which, in the articulated skull, is occupied by the pyramidal process of the 

 palate bone. In this fossa arises the internal pterygoid muscle, and at its 

 base is a slight depression, distinguished as the navicular fossa, which gives 

 attachment to the tensor palati muscle. 



Fig. 36. 



Fig. 36. THE SPHENOID BONK FROM BEFORE. f 



The indications where marked are the same as in the preceding figure. 17, marks the 

 anterior opening of the Vidian foramen or canal ; 18, the external or temporal surface of 

 the great wing; 19, its orbital surface; 20, the sphenoidal turbinated or spongy b one ; 

 above 20, the opening into the sphenoidal sinus ; 21, the sphenoidal spine ; 22, the 

 rostrum, and above 22, the inverted laminae, which fit with the edges of the vomer. 



FISSURES AND FORAMINA. Each lateral half of the bone presents a 

 fissure, four foramina, and a canal. The sphenoidal fissure is the obliquely 

 placed elongated interval between the great and the small wing ; it is closed 

 externally by the frontal bone, so as to form the foramen lacerum orbitale ; it 

 opens into the orbit, and transmits the third, fourth, and sixth nerves, the 

 ophthalmic division of the fifth nerve, and the ophthalmic vein. Above and 

 to the inside of it is the optic foramen, which, is inclined outwards and 

 forwards from the side of the olivary process, pierces the base of the small 



