THE SKULL. 



•29 



The Pterygoid Bones. 



Tlie jiterygoid bones in DiiKJCcrus luijubile (number lOofi), are opplied 

 to the inner surface of tlie palatines, and to the pterygoid plates of the 

 alisphenoid (Plate V, jit). They appear to unite on the median line in the 

 roof of the posterior nares, but the sutui-e is not distinct. The suture with 

 the palatine is oblique, and that with the alis])henoid can be traced ujiward 

 beneath the zygomatic arch. 



The lower margin of the pterygoid is thickened, and nearly straight 

 The posterior margin is thiimer, and moderately curved. 





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i 



FiGiTBB 30 — Horizontal sec'ion of skull of Tinoceras crassifrons. Marsh (No. 1230. 



f^'iGURE 3!. — Horizontal section of skull of Dinoceras iHstans, Marsli (Xo. I(i01). 



a c.ivily beliiud base of ci nine tootli ; J. l)rain-cavity ; c. alve 'le of canine tooth ; /. anterior olfactory 

 chaniliur; /'. posterior olfactory chamber; m'. maxillary protuberance; n. nasal bones; n'. nasal 

 protuberance ; }''■ parietal protuberances. 



Both figures are one-eiglith natural tize. 



