. The Ceratopsia. Ceratopsia. Fig. 36.—A, externa! view of right dentary of type of Triceratops flabellatus, No. 1821, Yale Museum; B, internal view of same, c, Coronoid process; af, dental foramina; sp, surface for predentary; ss, symphyseal surface; mf, mandibular fossa. One-eighth natural size. These are very long, thin bones, especially slender an- teriorly. They reach to the symphyseal border in front, and posteriorly they inclose internally and inferiorly the. mandibu- lar fossae. Throughout their entire length they are closely applied to the dentary, though they seldom even in the old i
. The Ceratopsia. Ceratopsia. Fig. 36.—A, externa! view of right dentary of type of Triceratops flabellatus, No. 1821, Yale Museum; B, internal view of same, c, Coronoid process; af, dental foramina; sp, surface for predentary; ss, symphyseal surface; mf, mandibular fossa. One-eighth natural size. These are very long, thin bones, especially slender an- teriorly. They reach to the symphyseal border in front, and posteriorly they inclose internally and inferiorly the. mandibu- lar fossae. Throughout their entire length they are closely applied to the dentary, though they seldom even in the old individuals, become coossified with it. In the middle and posterior reo-ion of the splenial the superior margin is expanded and overlaps the internal surface of the dentary above the lateral border of the mandibular fossa. Posteriorly, a little beneath the superior margin, there is a long slit dividing the posterior portion of the splenial into a broad, long inferior branch and a shorter and narrower superior. This slit or fissure is homologous with the internal mandibular foramen in the crocodile. It is inclosed behind by the articular. The inferior and larger of the two posterior branches of the splenial overlaps the angular throughout the entire length of the latter bone. THE Fig. 37.—Internal view of left splenial of type of Triceratops prorsus, No. 1822, Yale Museum, a, Anterior end; p, pos- terior; imf, internal mandibular foramen. One-eighth natural size. This is a broad, thin bone, convex on its inferior or external surface and concave above where posteriorly it receives the articular and sur- angular, while its thinner and narrower anterior portion overlaps the dentary, passing within the mandibular fossa and forming a portion of its postero-inferior wall. The external border of the angular is the thicker and is in contact throughout with the surangular, while medially it is produced into a rounded angle which fits into a corresponding pocket or groove in
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