AVillistox.] Mosasaurs. 121 



exoccipital and petrosal begins at the angle of the basioccipital 

 bone, curves backward through the meatus auditorius, and 

 thence toward the posterior margin of the distal extremity, lying 

 on the front margin of the stapedial groove for nearly its whole 

 length. The upper surface of the suspensorium is composed 

 chiefly of the exoccipital. The bone unites broadly with the 

 squamosal at its anterior surface side distally and sometimes 

 helps form a part of the quadrate articular surface. As regards 

 the relation which the exoccipital or paroccipital bears to the 

 quadrate, Baur says : " The Mosasauridse agree with the Iguana, 

 etc., in not having any part of the articular face for the quad- 

 rate on the paroccipital" ; Cope, that "the articulation of the 

 quadrate in the Pythonomorpha is exclusively with the paroc- 

 cipital [/. e., squamosal] and the squamosal [prosquamosal] ." 

 The fact is, that in some Mosasaurs both the paroccipital and 

 squamosal of Baur, or the exoccipital and paroccipital of Cope, 

 articulate with the quadrate, though the articular surface for 

 the former is always less extensive than that for the latter. 53 



In Platecarpus , at least, there is an elongate, conical or pyra- 

 midal process intercalated between the exo-paroccipital and the 

 petrosal, reaching nearly to the brain cavity. In nearly all of 

 the rare cases in which the squamosal is separated from the 

 suspensorium, this process is broken off from the body of the 

 bone at the extremity of the petrosal, the strongly roughened 

 surfaces appearing as though the bone terminated there, which 

 is not the case^j/The elongated portion that is thus intercalated 

 between the two bones is entirely excluded from the exterior, 

 received in a depression on the anterior superior face of the 

 exoccipital and completely overlapped by the petrosal. Inter- 

 nally, above, the suture of the supraoccipital extends outward 

 in a thin, rounded plate, as far as the lateral margins of the 

 condyle. The process extending downwards on the sides of the 

 basioccipital hypapophyses is broad and long, reaching as far 

 as the margin of the distal surface. Above, the short sutural 

 surface for the petrosal, between that for the supraoccipital 



53. This fact is also stated by Baur : " The lower and distal part of the paroccipital process 

 joins the quadrate." Journ. Morph., VII, 12, 1892. 



