ON THE SKULL AND THE BRAIN OF TRICERATOPS, 

 AVITH NOTES ON THE BRAIN-CASES OF ICxUANODON 

 AND MEGALOSAURUS. 



By Oliver P. Hay, 



Of W(ishhi(/t()n, />i.strict of ('oliiiiihia. 



Two circumstances recently stiniulatecl the writer to make a study 

 of the skull of the Ceratopsia. One of these was the sight of a nearly 

 complete brain-case of a sj)ecimen that has been identified as Tricera- 

 tops serratns (Cat. No. 241G, U.S.N.M.) j the other was the appear- 

 ance of Hatcher's monograph entitled The Ceratopsia, which was pub- 

 lished in 1907 as Monograph 49 of the U. S. Geological Survey. 



Inasmuch as some statements are made in Hatcher's monograph 

 regarding the structure of the skull of the Ceratopsia from which 

 the writer must dissent, it is desirable to express admiration for that 

 important work. For the first time there is brought together all that 

 is known about these bizarre reptiles. They form a difficult subject 

 of investigation, and no one writing about them can expect either to 

 avoid errors or to exhaust the subject. Therefore, every student of the 

 group needs to look with charity on the shortcomings of others. We 

 are under the highest obligations to Hatcher, Marsh, and Lull, as 

 authors of The Ceratopsia. 



The principal difficulty in the way of explaining the brain-case of 

 the Ceratopsia is found in the thorough coossification of most of the 

 component bones. Such is the condition of the brain-case referred to 

 in the first paragraph of the present paper. This specimen (Plate 1, 

 fig. 1; Plate 2, fig. 1) was collected for Professor Marsh in 1889 by 

 O. A. Peterson, on Lance Creek, Converse County, Wyoming. It is 

 not mentioned in The Ceratopsia under T . serratus, but Hatcher's figs. 

 32 and 34 were taken from casts which cepresent the brain that once 

 filled that specimen. In the legend under these figures the number 

 of the specimen is given as 20G5, but this is the accession number in 

 Marsh's collection, not that of the U. S. National Museum. 



As stated, most of the Ixmes are united so as to abolish all traces 

 of the sutures. However, the anterior, or orbitosphenoidal, segment 

 has remained free from that behind, as will be shown. 



Proceedings U.S. National Museum, Vol, XXXVI-No. 1660. 



i)5 



