1 34 SKELETON. 



or azygous process, for articulation with the vomer, and with 

 the nasal septum of the ethmoid. On each side of this process, 

 in front, is the orifice of the sphenoidal cell. These cells con- 

 sist, most commonly, of one on each side, and are separated 

 by a bony partition. In the very young bone they are not 

 formed. The body of the sphenoid undergoes so many changes 

 between early infancy and adult life, by the conversion of its 

 diploic structure into sinuses or cells, and is also so much mo- 

 dified in different individuals, that a general description of it 

 will not answer for all specimens. 



The two great wings arise from the sides of the body of the 

 sphenoid, by a small irregular base. From their lower part pro- 

 ject downvvards,on either side, the two pterygoid processes called 

 external and internal. These processes have a common base, 

 are partially separated behind by a groove called pterygoid fossa, 

 and below by a notch. The internal is the longest, and is termi- 

 nated by a hook, on the outer side of which is a trochlea made 

 by the tendon of the circumflexus muscle. The external ptery- 

 goid process is the broadest. By applying together the temporal 

 and sphenoid bones, a groove, common to the two, leading to 

 the Eustachian tube, will be seen. This groove is continued 

 obliquely across the root of the internal pterygoid process, and 

 indicates the course of the cartilaginous portion of the Eusta- 

 chian tube. The internal pterygoid process sends out from its 

 base a small shelf of bone, separated by a fissure from the un- 

 der part of the body of the sphenoid. The posterior edge of 

 the vomer rests against this projection. The fissure is filled up 

 in advanced life. 



The great wings of the sphenoid bone present three faces. 

 One is anterior, and called orbital, from its forming a part of the 

 orbit; another is external, and called temporal; and the third is 

 towards the brain, and forms a considerable part of the fossa 

 for containing its middle lobe. The orbital face is square and 

 slightly concave. The temporal face is an oblong concavity, at 

 the lower part of which is a triangular process, giving an origin 

 to the external pterygoid muscle. The cerebral face is concave 

 and marked by the convolutions of the brain, as well as by a 

 furrow made by the principal trunk of the great artery of the 

 dura mater as it passes from the temporal bone to the temporal 

 angle of the parietal. The inferior portion of the great wing is 



