Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/91

1869.] Upwards and backwards the same region of the præmaxilla passes into its anterior ascending process, which is 0⋅7 inch long, and becomes very slender above. Each uniting by harmonia, but not ankylosing, with its fellow, the two lie between, and separate, the inner edges of the nasal bones for a certain distance. Behind the nasal aperture the præmaxilla rises into its posterior process, which is about as long as the anterior, but has a much greater breadth. The posterior margin of the process, and of the body of the bone below it, is concave, rounded, and must have been quite loosely united with the anterior edge of the maxilla.

Five teeth with lanceolate acuminated crowns (fig. 3) lie close together in the præmaxilla, occupying a distance of 0⋅55 inch from its posterior end; but the alveolar margin of the "beak," which is continued in front of this, presents no indication of the presence of teeth. The maxilla is imperfect behind. So much of it as remains measures 1⋅5 inch in length, and rather more than half an inch in depth, posteriorly, where it is deepest. It bears ten teeth. The crowns of the anterior eight are well preserved; but the two hindermost are broken, only the section of the fang of the last being visible. The anterior four teeth are rather smaller than the others; and this is especially true of the first tooth. The anterior edge, of the crown of each of these teeth slightly overlaps the posterior edge of the crown of its predecessor. In the fifth, sixth, seventh, and eighth teeth, the overlap seems to have taken place in the opposite direction, the hinder edge of each tooth projecting a little beyond the anterior edge of its successor. The teeth are imbedded by single fangs, and, judging from the hindermost, are lodged in distinct alveoli. In unworn teeth the summit of the crown is sharp, and has a curved contour, which is more convex downwards in the anterior than in the posterior teeth. The free edge of the crown presents no trace of the serrations which are so characteristic of the teeth of Iguanodon; but it is sinuated by the terminations of sundry strong ridges of the enamel (fig. 2), which start from a sort of cingulum at the junction of the crown with the fang and, somewhat diverging and diminishing in thickness, traverse the outer surface of the crown. The cingulum is sharply angulated upwards in the three anterior teeth; but the angle becomes obtuse in the hinder teeth. The principal enamel ridge proceeds from the open angle of the cingulum, or a little behind it, to the crown. Secondary ridges of less prominence, which may not reach the cingulum, subdivide the spaces on each side of the principal ridge; and between them there are still shorter tertiary ridges, which do not extend more than halfway from the free edge towards the fang of the tooth. The sixth tooth is that the crown of which is most worn down, the other teeth being to all appearance less worn as they are further from it. The planes of the worn surface of the crowns, as in Iguanodon, cut the axis of the tooth at an acute angle, looking inwards as well as downwards. The outer contours of the teeth are convex from above downwards, but hardly so much so as in Iguanodon.

At first sight, these teeth look very similar to those of Iguanodon;