THE SKULL THE CEANIUM 



271 



walls of the sinuses are usually distinct and placed low down ; they 

 may, however, be obscure or confined almost to the upper borders. 



The lower surface of the presphenoid sometimes exhibits a very 

 strong median keel. The internal and external pterygoid processes 

 present variations in size and form ; it should be remembered that they 

 are easily destroyed by maceration and cleaning. 



The groove on the lower surface of the posterior sphenoid which 

 separates the basisphenoid from the alisphenoid and lodges the Vidian 

 nerve in some specimens is but faintly marked. The course of the 

 small internal carotid artery toward the middle lacerated foramen is 

 occasionally indicated on the sphenoid by a short groove passing across 

 the base of the lingula from the angle of the large notch to the Vidian 

 groove. This groove with the groove on the superior surface of the 

 bulla in front of the smaller entotynipanic spine forms a small carotid 



canal. 



HUMAN SPHENOID BONE. 



By reason of its irregular shape, its many processes, and its com- 

 plex articulations with so many other bones, the sphenoid presents 

 more difficulties to the student than any other bone in the human 



FIG. 193. FIG. 194. 



UPPER VIEW OF THE SPHENOID BONE. 



1, sella; 2, olivary eminence; 3, clivus; 4, anterior 

 clinoid process ; 5, posterior clinoid process ; 6, posterior 

 border of the body; 7, cerebral surface of the great 

 wing ; 8, articular surface for the frontal bone ; 9, ar- 

 ticular border for the temporal bone; 10, spinous pro- 

 cess; 11, small wing; 12, border articulating with the 

 orbital plate of the frontal bone; 13, border joining 

 the ethmoid bone ; 14, optic foramen ; 15, sphenoidal 

 fissure ; 16, foramen rotuudum ; 17, foramen ovale ; 18, 

 foramen spinosnm ; 19, groove on the liugula for the 

 internal carotid artery. 



FRONT VIEW OF THE SPHENOID BONE. 



1, ethmoidal process ; 2, sphenoidal crest and ros- 

 trum for joining the nasal plate of the ethmoid bone 

 and the voiner; 3, entrance of the sphenoidal si- 

 nuses; 4, small wing; 5, optic foramen piercing its 

 base ; 6, sphenoidal fissure ; 7, foramen rotundum ; 

 8, orbital surface of the great wing ; 9, temporal sur- 

 face of the same; 10, ridge separating the tempo- 

 ral and zygomatic surfaces; 11, vaginal process; 

 12, Vidian canal ; 13, internal pterygoid plute ; 

 14, hamular process ; 15, external pterygoid plute ; 

 16, angular process ; 17, foramen ovale ; 18, fora- 

 men spinosum. 



skeleton. It will be readily understood if the more generalized type 

 has been first studied. 



Compared with the sphenoid of the cat, it is much compressed from 

 before backward, and thus appears to be relatively broader; it presents, 



