262 



MAMMALIAN ANATOMY 



The part contributed by the basisphenoid is easily distinguished 

 (Fig. 189). It consists principally of a central, flattened area, which 

 is quadrate, as long as it is wide, and slightly concave transversely, on 

 each side of the middle line. The anterior angles are cut off by the 

 rounded inner posterior angles of the pterygoid processes, leaving a 

 short straight transverse anterior border between them. The trans- 

 verse posterior margin is much wider and is very slightly emarginate 

 on each side of the median line ; the posterior angles are produced, 

 and each forms the inner lip of the large notch for the temporal. The 

 lateral boundaries of this flattened area are sharp longitudinal ridges 

 which run from its posterior angles nearly to the posterior margins of 

 the pterygoid plates. On each side a triangular roughened area is 



FIG. 189. 



With Presphenoid. 



With Pterygoid. 



With End of Bulla. 



WithEntotympanic. 



With Alisphenoid. 



With Basioccipital. 

 BASISPHENOID, OUTER OR LOWER SURFACE. 



mth p e t rous part of Temporal. 



included between this ridge and an oblique groove which runs inward 

 and forward from the notch on the outside of the lingula behind to 

 the foramen or slit just behind the pterygoid plate in front, This 

 area slopes slightly upward and outward and articulates with the 

 anterior end of the entotympanic portion of the auditory bulla. The 

 posterior margin of this triangular articular surface is, in general, trans- 

 verse, but is deeply incised by the temporal notch ; the inner margin 

 is longitudinal and bevelled. The outer margin, which is directed 

 forward and inward, is also bevelled, and is produced on the upper 

 surface as a more or less prominent ridge overlapping the anterior 

 angle of the notch and forming an outer boundary to a groove for the 

 carotid artery. 



The under surface of the pterygoid process (Fig. 190) is sharply 

 defined behind, only at its inner half, as a thin margin overlapping the 

 basisphenoid and rounding forward into the straight thin inner margin 

 which overlaps the presphenoid. This prolongation inward of the 



