MEGALOSAURUS. 271 



transverse section, fig. 11). Had the serrature continued along the 

 whole of the blunt and convex portion of the tooth, it would, in this 

 position, have possessed no useful cutting power ; it ceased precisely 

 at the point beyond which it could no longer be effective. In a tooth 

 thus formed for cutting along its concave edge, each movement of 

 the jaw combined the power of the knife and saw ; whilst the apex 

 in making the first incision, acted like the two-edged point of a 

 sabre. The backward curvature of the full-grown teeth, enabled 

 them to retain, like barbs, the prey which they had penetrated. In 

 these adaptations, we see contrivances, which human ingenuity has 

 also adopted, in the preparation of various instruments of art."(l) 



The teeth of the Megalosaur consist of a central body of dentine, 

 with an investment of enamel upon the crown, and of cement over 

 all, but thickest upon the fang. The marginal serrations are 

 formed almost entirely by the enamel, and when slightly magnified 

 are seen to be rounded, and separated by slight basal grooves (PL 62, a, 

 fig. 6, c) ; the smooth and polished enamel upon the sides of the 

 crown presents a finely wrinkled appearance ; the remains of the pulp 

 are converted into a coarse bone in the completely formed tooth. 



The dentine consists of extremely fine and close-set calcigerous 

 tubes, without admixture of medullary canals ; they radiate from the 

 pulp-cavity at right angles with the external surface of the tooth ; 

 the primary curvatures correspond with those of the calcigerous 

 tubes in the monitor's tooth (PI. 67) but are less marked, so that 

 the tubes appear straighter. They present a diameter of gsloooth of an 

 inch ; with interspaces varying between two and three times that 

 diameter ; they dichotomize sparingly, but the number of minute 

 secondary branches sent off into the intermediate substance is very 

 great. These secondary branches proceed at acute angles from the 

 primary tubes ; the divisions of the tubes become very frequent near 

 the periphery of the dentine and the terminal branches dilate into, or 

 inosculate with a stratum of calcigerous cells, which separates the den- 

 tine from the enamel. The microscopic characters of the tooth of the 

 Megalosaur are represented in PL 70 a, in part of a transverse sec- 



(1) Biidgewater Treatise, vol. i, p. 237. 



