THE SPHENOID BONE. 29 



uous with the crest ; it fits in the angle formed by the 

 diverging alae of the vomer. At each side are curved 

 ridges of bone, called the vaginal processes, for articula- 

 tion with the alse of the vomer. Between the vaginal 

 and pterygoid .processes is the pterygo-palatine groove, 

 which is formed into a canal by articulation with the 

 sphenoidal process of the palate ; it transmits the pterygo- 

 palatine vessels and the pharyngeal nerve. The pos- 

 terior surface, before the twentieth year, is covered by a 

 layer of cartilage which separates it from the basilar 



ftaygoU JiiJg, 



LAXATOR TYMPAMI 



Fia. 12. SPHENOID BONE, ANTERIOR SURFACE. 



process of the occipital. After the twentieth year this 

 cartilaginous plate ossifies, and the sphenoid and occipital 

 form one bone. Projecting from the sides of the upper 

 part of the body of the sphenoid are two thin, sabre- 

 like processes, the lesser wings. These are placed hori- 

 zontally, their surfaces looking up and down. The 

 anterior border is serrated for articulation with the or- 

 bital plate of the frontal. The posterior border is thin 

 and smooth, and is received in the fissure of Sylvius. 

 It projects at its inner posterior portion, and forms a 

 triangular process of bone called the anterior clinoid 



