THE SKULL. 29 



not been taken in preparing the skull), which 

 separates the cranial cavity from the internal 

 ear. The extent of this plate varies very much, 

 being less in older specimens. The corner of 

 the supra-occipital which bounds it above, rep- 

 resents the epiotic bone (39). 



f. Behind the cartilage is the opisthotic bone, and 

 in front of it the prootic. 



g. In front of the supra-occipital and prootic, and 

 also reaching back so as to cover in a part of 

 the supra-occipital, is the parietal bone, and be- 

 tween it and the prootic, the large foramen 

 {foramen ovale) for the exit of the main di- 

 visions of the trigeminal nerve. 



h. External to the anterior clinoid process of the 

 basi-sphenoid, and in the prootic bone, is seen 

 the opening of the canal through which the 

 internal carotid artery enters the cranial cav- 

 ity. • Pass a probe back through the canal to 

 the point where the common carotid artery 

 enters the skull cavity (26, e). 



i. In front of the basi-sphenoid is seen the ptery- 

 goid bone, forming that part of the base of the 

 skull. 



k. External to the pterygoid, below the parietal, 

 and in front of the prootic, is the small ali- 

 sphenoid bone. 



/. In front of the descending plate of the parietal 

 (45) is the large aperture left by the removal of 

 the membranous interorbital septum in prepar- 

 ing the skull. Bounding it behind is the parie- 

 tal ; above, the frontal and the naso-prefrontal 

 bones; in front, the naso-prefrontal; below, the 



