THE SKULL THE CEANIUM 



199 



upward, and inward ; and the inferior surface faces downward, for- 

 ward, and outward. These surfaces are separated by three borders, 

 the posterior border, which joins the outer edge of the basilar plate 

 of the occipital ; the anterior border, which joins the basisphenoid, the 

 alisphenoid, and the squamous portion ; and the superior border, which 

 is in part applied to the under surface of the tentorium and in part 

 exposed in the cranial cavity (Fig. 134). The apex of the petrous 

 overlaps the inner posterior cranial portion of the basisphenoid at 

 the large lateral notch. The posterior surface is the only one plainly 

 visible in the cranial cavity, where it assists in the formation of the 

 sides of the posterior cerebral fossa. 



FIG. 135. 



Sguamosal, with Parietal. 



Zygomatic Process. 



On Eoof of Tympanum., 



Ridge marking inner edge of 

 portion of Petrous covered 

 by Tentorium. 



Fossa for Appendicular Lobe 



of Cerebellum. 

 Over Superior Semicircular 



Canal. 



Over Posterior Semicircu- 

 lar Canal. 



Part of Middle Cerebral Fossa. 

 With Alisphenoid. 



With Occipital. JN 



Mastoid. 



Pit for Dura. 



Aquxductus Cochleae. 



Internal Auditory tfeatus. 

 Outer Margin of Middle Lacerated Foramen. 



Hiatus Fallopii. 



Post-glenoid Process. 



Opening in roof of Tympanum. 



Groove for Eustachian Tube. 



With Basisphenoid. 



Apex of Petrous. 



Beginning of Aquxductus Fallopii. 



Bulla. 



LEFT TEMPORAL BONE, INNER ASPECT. 



The posterior surface (Fig. 135), although marked by depres- 

 sions and elevations, lies all in one plane. Its general outline is tri- 

 angular, and it is nearly twice as long as it is wide. The base of 

 the triangle lies above and behind, against the squamous and mastoid ; 

 its sides are the anterior and posterior margins. The anterior margin 

 is arcuate or slightly sinuate, and well defined for the outer two-thirds 

 and faintly emarginate for the inner third, where the posterior and 

 anterior surfaces pass into each other. The posterior margin is gently 

 arcuate, especially at the apex of the surface, which thus appears 

 turned slightly outward. For most of its course the posterior boundary 

 is in contact with the basioccipital and faces as much inward as back- 



