WEALDEN FORMATIONS. 23 



which have a like endless succession of teeth, is the deeper position of the successional 

 tooth in relation to the one it is destined to replace, and the great proportion of the 

 tooth which is formed before it is protruded. This interesting character is well 

 exhibited in a portion of the jaw, kindly submitted to rny examination by His Grace 

 the Duke of Marlborough, and which is figured in T. XI, fig. 1. The anterior tooth, 

 a, in this specimen, shows, at the inner side of its base, the commencing absorption 

 stimulated by the encroaching capsule of the successional tooth below, the crown of 

 which is completed externally, though not consolidated. On one of the fractured 

 margins of this piece of jaw a part of the basal shell of an absorbed and shed tooth 

 remains at a, fig. 3, with part of the root of the successional tooth which has risen into 

 place, b ; but which shows its base full of matrix, the pulp not having been calcified 

 at that period of the tooth's growth. The crown of a third tooth, c, incompletely 

 calcified, is exposed beneath, in the substance of the jaw. In fig. 1, the germs of 

 several successional teeth are shown at c. In the proportion of the successional teeth 

 which is calcified in the formative cavity in the substance of the jaw, the Megalosaurus 

 offers a closer resemblance to the Mammalian class than do any of the recent or extinct 

 Crocodilian or Lacertian reptiles. But the evidence of uninterrupted and frequent suc- 

 cession of the teeth in the Megalosaurus is unequivocal, and this part of the dental 

 economy of the great carnivorous Reptile is strictly analogous to that which governs 

 the same system in the existing members of the class. The different forms of the teeth at 

 different stages of protrusion did not fail to attract the attention of the gifted discoverer 

 of the Megalosaurus, in whose words I will conclude this part of my Monograph on the 

 most formidable of extinct British Reptiles. 



" In the structure of these teeth 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, 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 form, like that of the two-edged point of a sabre, cutting 

 equally on each side. As the tooth advanced in growth it became curved backwards 

 in the form of a pruning-knife, and the edge of serrated enamel was continued down- 

 wards to the base of the inner and cutting side of the tooth, whilst on the outer side a 

 similar edge descended but a short distance from the point, and the convex portion of 

 the tooth became blunt and thick, as the back of a knife is made thick for the purpose 

 of producing strength. The strength of the tooth was further increased by the 

 expansion of its side. 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 



