DINOSAURIA 263 



"In the structure of these teeth we find a conibinadon 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 cur\ i s< I 

 backwards in the form of a pruning-knife, and the edge of 

 serrated enamel was continued downwards 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 pro- 

 ducing strength. The strength of the tooth was further incr< sased 

 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 teeth enabled them to 

 retain, like barbs, the prey which they had penetrated. In th< sse 

 adaptations we see contrivances which human ingenuity has 

 also adopted in the preparation of various instruments of art." " 

 The oldest known beds from which any remains of Mcgalo- 

 saurus have been obtained are the lower oolites at Selsby Hill, 

 and (Jhipping-Norton, Gloucestershire. Abundant and charac- 

 teristic remains occur in the Stonesfield slate, Oxfordshire 

 Teeth of this genus have been found in the Cornbrash and 

 Bath oolite ; both teeth and bones are common in the Wealden 

 i; Buckland, " Bridgewater Treatise," p 236. 



