THE SPHENOID BONE. 31 



head of the external rectus muscle; occasionally, the 

 inferior rectus also has a point of origin close to the 

 lower head of the external rectus. One or two small 

 foramina are occasionally observed ; they transmit small 

 vessels. The plane of the anterior surface is directed 

 nearly vertically ; it looks obliquely forward and inward, 

 and forms the outer posterior wall of the orbit. The 

 external surface is divided by the pterygoid ridge into a 

 superior and an inferior portion. The superior surface 

 forms part of the side of the skull, and is about an inch 

 and a half long by one-half to three-fourths of an inch 

 broad. It is concave from before backward, and assists 

 in forming the temporal fossa. A few small foramina 

 are seen which transmit small, nutrient vessels. The 

 inferior surface extends from the pterygoid ridge to 

 the base of the pterygoid process, and assists in forming 

 the roof of the zygomatic fossa. The pterygoid ridge is 

 about an inch and a half long, and runs from the orbital 

 plate to the spine of the great wing. The upper an- 

 terior margin of the greater wing articulates with the 

 frontal ; the upper posterior portion articulates with the 

 anterior inferior angle of the parietal. The posterior 

 border articulates ' with the squamous portion of the 

 temporal. The spine is received into the angle between 

 the squamous and petrous portions of the temporal 

 bone. The anterior border of the orbital surface articu- 

 lates with the malar. 



The pterygoid processes are two strong, somewhat 

 irregular processes of bone, consisting each of two plates 

 of bone joined anteriorly. Each process arises from the 

 under surface of the body and greater wing, and is 

 directed vertically downward. At the base of the ptery- 

 goid process is the Vidian canal; it passes horizontally 

 backward above its root. This canal transmits the 



