104 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 55. 



Wyoming. On account of the absence of all the essential external 

 portions such as the horn-cores, nasals, premaxillaries, and most of 

 the squamosals, I am unable to determine the species to which this 

 specimen belongs. It serves, however, to graphically illustrate the 

 internal structure of the Ceratopsian skull, and especially the rela- 

 tively small size and position of the brain cavity, and the large over- 

 lying sinuses. 



A study of this sectional skull in conjunction with the posterior 

 portion of the cranium of a second individual (Cat. No. 6679, 

 U.S.N.M. ; see Plate 7.) Triceratops species, and the disarticulated 

 skull of Brachyceratops 7nontanensis (Cat. No. 7951, see fig. 4) en- 

 ables me to verify the work of other authors and in some instances to 

 point out where they were in error. Commencing with the frill I think 

 all authorities are agreed that the lateral bones are the squamosals. 

 It is the median part of the frill that has been the subject of much 

 discussion and a variety of interpretations. Marsh first identified it 

 as the fused parietals, and he has been followed by most writers on 

 the subject. Hay^ showed that this identification could not be ac- 

 cepted and suggested that it might represent the fused supratem- 

 porals or possibly the coalesced nuchal bones. Huene ^ identified the 

 anterior end of this central portion as parietal and the posterior end 

 as a dermosupraoccipital, but it has been pointed out that this con- 

 clusion is not altogether acceptable. Gilmore^ in describing the 

 skull of Brachyceratops reached the conclusion that the parietal was 

 entirely excluded from the dorsal surface of the skull in that genus — 

 a conclusion verified by Brown * in a later study of other Ceratopsiam 

 slmlls. In the article cited above Brown also concludes that the 

 median part of the frill represents the " fused postfrontals." The 

 study of the disarticulated Brachyceratops skull which has the post- 

 frontal bones entire (see fig. 4), shows conclusively that they do not 

 extend backward to form any part of the crest. In fact a compari- 

 son of the top of the Brachyceratops skull with a Monoclonius skull, 

 figured by Brown ^ shows a transverse line between the supratem- 

 poral fossae, separating their posterior ends from the frill portion 

 as in Brychyceratops although it is not there recognized as a suture. 

 That a suture does exist at this point is abundantly shown by sev- 

 eral skulls and numerous separate frills. That the conclusion reached 

 by both Gilmore and Brow^n that the parietal does not show on the 

 dorsal surface of the skull is further substantiated by specimens 

 Nos. 5740 and 6679, particularly the latter, which shows the parietal 

 as extending upward and backward as a thin sheet of bone under- 



iProc. U. S. Nat. Mus., vol. 36, 1908, pp. 95-108. 



sNeues Jahrbuch, vol. 11, 1911, pp. 146-162. 



» Smiths. Mihc. Coll., vol. 63, No. 3, 1914, p. 7. 



* Bull. Amer. Mus. Nat. Hist., vol. 83, October, 1914, p. 543. 



» Idem, vol. 34, October, 1914, pp. 549-558, fig. 1. 



