MEGALOSAURUS. 183 



teeth, (PI. 23, Figs. ] '— 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 Gan- 

 geticus. 



As in all animals, the jaws and teeth form the most cha- 

 racteristic parts, I shall limit my present observations to a 

 few strikinfT circumstances in the dentition of the Mejialo- 

 saurus. 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 thev 

 were designed. Their form and mechanism will best be 

 explained by reference to the figures in PI. 23.* 



In the structure of these teeth, (PI. 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, (PI. 23, Figs. I'. 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 juw (PI. 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 (PI. 23, Fig. 1') throws up a scries of triangular plates of 

 bono, forming a z'g-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 ncwteuth 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 coiiirjvance for the renewal of teeth is 

 strictly analogous to that which takes place in the dentition of many species 

 of existing Lizards. 



