teeth, (Pl. 23, Figs. 1'—2'.) The form of this jaw shows that the head was terminated by a straight and narrow snout, compressed laterally like that of the Delphinus Gangeticus.
As in all animals, the jaws and teeth form the most characteristic parts, I shall limit my present observations to a few striking circumstances in the dentition of the Megalosaurus. From these we learn that the animal was a reptile, closely allied to some of our modern Lizards; and viewing the teeth as instruments for providing food to a carnivorous creature of enormous magnitude, they appear to have been admirably adapted to the destructive office for which they were designed. Their form and mechanism will best be explained by reference to the figures in Pl. 23.[1]
In the structure of these teeth, (Pl. 23, Figs. 1, 2, 3,) we find a combination of mechanical contrivances analogous to those which are adopted in the construction of the knife, the sabre, and the saw. When first protruded above the gum, (Pl. 23, Figs. 1'. 2'.) the apex of each tooth presented a double cutting edge of serrated enamel. In this stage, its position and line of action were nearly vertical, and its
- ↑ The outer margin of the jaw (Pl. 23, Fig. 1'. 2'.) rises nearly an inch above its Inner margin, forming a continuous lateral parapet to support the teeth on the exterior side, where the greatest support was necessary; whilst the inner margin (Pl. 23, Fig. 1') throws up a series of triangular plates of bone, forming a zig-zag buttress along the interior of the alveoli. From the centre of each triangular plate, a bony partition crosses to the outer parapet, thus completing the successive alveoli. The new teeth are seen in the angle between each triangular plate, rising in reserve to supply the loss of the older teeth, as often as progressive growth, or accidental fracture, may render such renewal necessary; and thus affording an exuberant provision for a rapid succession and restoration of these most essential implements. They were formed in distinct cavities, by the side of the old teeth, towards the interior surface of the jaw, and probably expelled, them by the usual process of pressure and absorption; insinuating themselves into the cavities thus left vacant, This contrivance for the renewal of teeth is strictly analogous to that which takes place in the dentition of many species of existing Lizards.
