16 



THE CERATOPSIA 



but a small portion of the inferior margin of the jaws. There is no septum formed of the premax- 

 illaries and nasals partially dividing the nares, although it is present in the Ceratopsidae. As usual, 

 however, the premaxillaries enter into the profile of the muzzle between the limits of the rostral 

 and the nasals. An unusual feature among Ceratopsia, found elsewhere only in Leptoceratops, is the 

 possession of a pair of cylindrical teeth in close mutual contact on either side of the muzzle just behind 

 the rostral border. The nares are elongated ellipses with their long axes directed upward and 

 backward at an angle of about 45° from the perpendicular. 



The maxillaries, together with the jugals, are the largest bones of the face. They are roughly 

 triangular in form, being bounded in front by the premaxillaries, above by the lacrymals, and for a 

 very brief space by a downwardly projecting process of the nasals. Posteriorly, the maxillaries are 

 bounded by the jugals and pterygoids. Inferiorly, there is an unusually long, edentulous margin 

 before the tooth row is reached. The number of dental alveoli is 13 to 15, and, because there are 

 but two horizontal rows of successional teeth, there is no such deep alveolar groove as that seen in 

 the later ceratopsians. The preorbital fossa forms a not very deep depression on the side of the face, 

 and includes within its area about equal moieties of the maxillary and lacrymal bones. The actual 

 foramen (lacrymal foramen of authors) is much smaller and lies within the lacrymo-maxillary suture. 

 This fossa is reduced to a narrow slit in the later ceratopsians. Mr. Granger thinks it may have 

 lodged a facial gland, possibly hedonic, like those found within either ramus of the lower jaws in 

 the Crocodilia. This is, however, a matter of pure conjecture, and the gland would of necessity 

 become practically vestigial in later forms. What then would be its utility? The foramen is appar- 

 ently the vestige of the preorbital opening, large in saurischian dinosaurs, but always reduced in the 

 Ornithischia. 



The nasal bones meet in a median suture throughout, without the customary fusion seen in most 

 later genera. Anterior to the nares there is a slender process which meets an ascending process of the 

 premaxillary. There is the suggestion of a prominence about mid-length of the nasals, with a con- 

 centration of the grain of the bone toward it, seemingly foreshadowing the coming of a nasal horn. 

 There is a median longitudinal depression on the nose, reaching back beyond the limits of the frontals 

 in specimen No. 6408, but less pronounced in No. 6429. The nasals are bounded by the premax- 

 illaries in front and below, with an area of contact with the maxillaries, of varying width, followed by 

 that with the lacrymal and prefrontal bones. At their hinder end, they articulate with the frontal 



bones. . . 



The complex of bones surrounding the orbit has been subject to varied interpretation. It is 

 generally assumed that the true frontals, as discrete bones, do not appear on the surface of the skull 

 in the later ceratopsians in which the secondary roofing has been developed. One would expect to 

 find them, however, in Protoceratops, and probably in Leptoceratops, in which the secondary roofing 

 is incomplete. I should interpret the pair of bones lying between the orbits on the dorsal surface of 

 this skull as frontals, flanked in front and behind the orbit by the prefrontals and postfrontals 

 respectively, the "freely articulating palpebral bones" of Gregory and Mook representing the supra- 

 orbitals. The prefrontal lies above the lacrymal, the suture between them being clearly visible in 

 the skull under discussion. They form the anterosuperior border of the orbit except where excluded 

 therefrom by the palpebral bones. Above and anteriorly, the prefrontals are bounded by the nasals, 

 and posteriorly by the frontals which form the superior orbital border. Nowhere is the rim of the 

 orbit thickened as in later ceratopsians, for this is a defensive modification concomitant with the devel- 

 opment of horns. The postfrontal bones bound the orbit on the rear and articulate in turn with the 

 frontals above, the squamosals behind, and the jugals below. Near the junction with the postfrontals, 

 the frontals become somewhat roughened, and over the suture, especially on the right side of the 

 skull, there appears once more a decided prominence suggestive of the brow horn yet to come. There 

 is no trace of the pineal foramen nor of the pseudo-pineal fontanelle which is seen only in forms with 

 the secondary roofing and may disappear even in them, as in the type of Triceratops prorsus. The 

 absence of the true pineal foramen casts doubt upon Gilmore's interpretation of an aperture in the 

 roof of the actual brain case of Triceratops* below the secondary roofing. (See p. 72, Fig. 31.) 



4 Gilmore, C. W., 1919, B, p. 107, Fig. 1. 



