| OCR Text |
Show 180 DR. A. S. WOODWARD ON EXTINCT [Mar. 5, clear that they are gently recurved, aud fragments show that the anterior border is serrated for more than half its length below the apex at least in the first and third teeth. No successional teeth are visible. Of the maxilla (mx.) only the oral border and some of its teeth remain. That of the right side is most extensively preserved, and bears seven of its teeth in a rather fractured state. Its outer face is flattened aud does not exhibit any large vascular foramina. Its inner face does not bear any palatal extension. The teeth are arranged in a moderately spaced series, and fixed in distinct sockets, of which the inner wall is as much elevated as the outer wall and does not exhibit any vertical clefts. All the teeth are much laterally compressed, with a median indentation on each side near the base; and their long diameter exactly coincides with the long axis of the maxilla. The apex of the fully extruded teeth is much recurved. The marginal serrations, as in the premaxillary teeth, are disposed at right angles to a tangent to the border; and in the fifth tooth at least they are shown to extend for considerably more than half the length of the anterior border from the apex. The posterior border of the fourth tooth displays serrations as far as its base. The middle teeth are especially large and elevated, the height of the fourth and fifth being about one and two-thirds times that of the fourth premaxillary tooth. All the teeth, indeed, are larger and more laterally compressed than those of the premaxilla. Successional teeth are shown to arise at the inner side of the base of the functional teeth. One has just displaced the third maxillary tooth on the left, and another the seventh maxillary tooth on the right; while the second right maxillary tooth is not completely extruded. N o other successional teeth are seen. The mandible is represented only by its anterior half or dentary region, which is nearly similarly preserved on both sides. The rami must have been very loosely united at the symphysis, the symphysial facette being apparently narrow and smooth. The dentary bone (d.) is almost as deep as the premaxillae and does not taper to the symphysis, where its inferior angle is rounded off, but probably less so than is indicated in the side view of the imperfect fossil. Its oral border must have been nearly straight, while its lower margin, which is satisfactorily preserved, seems to trend slightly downwards behind, where the bone becomes thinner. The teeth are shown to be inserted in complete and distinct sockets, with the inner wall as high as the outer wall, and neither cleft nor pierced by nutritive foramina. The upper inner border of the dentary bone itself, however, is much fractured and not well exposed; while the actual upper edge of the inner wall of the tooth-sockets is formed by a small and loosely-apposed, laterally compressed rod of bone (fig. 1 a, spl.), which doubtless corresponds with the curious anterior extension of the splenial described by Marsh in Ceratosaurus1. The teeth of the mandible are comparatively small, none being larger than those of the premaxilla. 1 O C. Marsh, "The Dinosaurs of North America" (16th Ann. Rep. U.S. Geol. Surv. 1896), p. 159. |
