504 0. C. Marsh — Skull of the Gigantic Ceratopsidm. 



The frontals form the central region of the skull, and have 

 been greatly strengthened to support the enormous horn-cores 

 which tower above them. These elevations rest mainly on the 

 frontal bones, but the supra-orbitals, the post-orbitals, and the 

 post-frontals, have, apparently, all been absorbed by the 

 frontals, to form the solid foundation for the horn-cores. 



These horn-cores are hollow at the base, and in form, posi- 

 tion, and external texture, agree closely with the corresponding 

 parts of the Bovidw. 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 out- 

 line, and of moderate size. Its position and form are shown 

 in Plate XII, figure 1, b. 



The enormous posterior crest is formed mainly by the 

 parietals, which meet the frontals immediately behind the 

 horn-cores. The 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 of 

 the crest, may be called the epoccipital bones (Plate XII, 

 figures 1 and 2, 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 frontal elements which form the base 

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

 supra-temporal fossae lie between the squamosals and the 

 parietals, as shown on Plate XII, figure 2, c. 



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 

 foramen magnum is very small, about one-half the diameter 

 of the occipital condyle. The brain-cavity is especially dimin- 

 utive, smaller in proportion to the skull, than in any other 

 known reptile. 



The exoccipitals are also robust, and firmly coossified with 

 the basi-occipital. The supra-occipital is inclined forward, 

 and its external surface is excavated into deep cavities. It is 

 firmly coossified with the parietals above, and with the exoc- 

 cipitals on the sides. The post-temporal fossae are quite small. 



