NO. 2260. 2^EW RESTORATION OF TRICERATOPS—GILMORE. Ill 



3. That the prefrontals and post f rentals which in the normal 

 reptilian skulls are lateral elements have in the Ceratopsian cranium 

 shifted their position from a lateral to a dorsal position supported 

 beneath by strong vertical buttresses. That such a change has taken 

 place is further indicated by the fact that in the older and more 

 primitive Ceratopsians the complete coalescence of the post- and 

 prefrontals of opposite sides on the median line has not always been 

 perfected, though I know of no Lance specimens where this complete 

 coalescence has not been completed. 



After a study of the brain case in Camptosaurus, Stegosaiirus, 

 TraeKodon^ Allosaurus^ and Triceratops it appears that no matter 

 how diverse the modifications of the external bones of the skull may 

 be, those forming the brain case have the same definite relations to 

 each other and to the brain itself. Lambe considered the postfrontal 

 as including nearly all of that portion of the skull between 

 the horn cores and an area on the lateral surface extending 

 down and back of the orbit to its inferior level. Huene correctly 

 recognized a portion of the lateral area posterior to the orbit as being 

 the postorbital and so it stood until the discovery of the Brarhycera- 

 tops skull which demonstrates conclusively that the postorbital in 

 that genus includes the horn above the eye and that the lateral exten- 

 sion of the postfrontals is not external but internal to the supra- 

 orbital horn cores, as shown in figure 4. I can hardly believe, in the 

 light of the Brachyceratops skull that the postorbital bone has been 

 so reduced in size in Triceratops as indicated by Huene. In a recent 

 paper by Lambe ^ the small bones interposed between the prefrontals 

 and identified as the frontals represented without question the for- 

 ward ends of the postfrontals. 



EXPLANATION OP PLATES. 



Plate 3. 



Life restoration of Triceratops elatus Marsti. Modelled by Charles W. Gil- 

 more 1915. Based on the mounted skeleton in the United States National 

 Museum, About one-twenty-eighth natural size. 



Plate 4. 



Skull and jaws of Trirrrnlnps ohtn.ttts Marsh. Type. No. 4720, U.S.N.M. 

 Viewed from the left side. About one-twelfth natural size. 



Plate 5. 



Fig. 1. — Series of eight articulated posterior dorsal vertebrae of Triceratops, 

 sp. No. 8091, U.S.N.M. About one-eighth natural size. Viewed from the right 

 side. The transverse processes of the left side are perfectly preserved. 



* Museum Bulletin No. 12, Canada Department of Mines, pi. 9, figs. 1 and 2, 1915. 



