170 O. C. Marsh — The gigantic Ceratojisidce, 



The frontal bones are quite short, and early nnite with each 

 other and with the adjoining elements, especially those behind 

 them. The frontal or central region of the skull is thus 

 greatly strengthened to support the enormous horn-cores which 

 tower above. These elevations rest mainly on the postfrontal 

 bones, but the supra-orbitals and the post-orbitals are also 

 absorbed to form a solid foundation for the horn -cores. 



These horn-cores are hollow at the base (Plate I, figure 3), 

 and in general form, position, and external texture, agree with 

 the corresponding parts of the Bovidoe. They vary much in 

 shape and size in different species. They were evidently 

 covered with massive, pointed horns, forming most powerful 

 and effective weapons. 



The orbit is at the base of the horn-core, and is surrounded, 

 especially above, by a very thick margin. It is oval in outline, 

 and of moderate size (Plate I, figure 1, h). 



The postfrontal bones are very large, and meet each other 

 on the median line. Posteriorly, they join the squamosals and 

 the parietals. At their union with the latter, there is a median 

 foramen (Plate I, figure 3, x) which apparently corresponds to 

 the so-called "parietal foramen."* In old individuals, it is 

 nearly or quite closed. When open, it leads into a large sinus, 

 extending above the brain-case into the cavities of the horn- 

 cores. This foramen has not before been observed in Dinosaurs. 



The enormous posterior crest is formed mainly by the 

 parietals, which meet the postfrontals immediately behind the 

 horn-cores. The posterior margin is protected by a series of 

 special ossifications, which, in life, had a thick horny covering. 

 These peculiar ossicles, which extend around the whole crest, 

 I have called the epoccipital bones (Plate I, figures 1-4, e). 

 In old animals, they are firmly coossified with the bones on 

 which they rest. 



The lateral portions of the crest are formed by the squamosals, 

 which meet the parietals in an open suture. Anteriorly, they 

 join the postfrontal elements which form the base of the 

 horn-core, and laterally, they unite with the jugals. The 

 supra-temporal fossse lie between the squamosals and the 

 parietals. 



The base of the skull has been modified in conformity with 

 its upper surface. The basi-occipital is especially massive, and 

 strong at every point. The occipital condyle is very large, and 

 its articular face, nearly spherical, indicating great freedom of 

 motion. The basi-occipital processes are short and stout. The 

 basi-pterygoid processes are longer and less robust. 



* The name usually applied to this aperture is misleading, as in Chameleo and 

 some other reptiles, the foramen is not in or near the parietal bones. It may 

 more properly be called the " pineal foramen." 



