THE TEMPORAL BONES. 



23 



against them. A penetration of the roof of the Glas- 

 serian fissure will enter the cranial cavity, and may 

 injure the inferior surface of the temporo-sphenoidal 

 lobes of the brain. The posterior wall is a frail partition, 

 formed by the vaginal process. It separates the glenoid 

 fossa from the external auditory canal. 



The petrous portion of the temporal bone is not seen 

 at the side of the skull. It springs from the inner sur- 

 face of the temporal bone, and projects forward and in- 



etfO.1 



-BrutU patud duvuyb CoMtui fatal 



FIG. 9. LEFT TEMPORAL BONE, INNER SURFACE. 



ward, forming an angle of 35 degrees with the squamous 

 portion of the bone. In shape, it is the frustum of a 

 trilateral pyramid lying upon its side. Its base is applied 

 to the inner surface of the squamous and mastoid por- 

 tions. It presents for examination an anterior, a pos- 

 terior, and an inferior surface, and an apex. The 

 anterior is smooth and polished, and presents, near its 

 junction with the squamous portion, an elevation which 

 marks the position of the superior semi-circular canal. 

 Below this is a depression, beneath which is the tym- 



