MEGALOSAURUS. 239 
backwards, in the form of a pruning knife, 
(PI. 23, Figs. 1. 2. 3,), and the edge of serrated 
enamel was continued downwards to the base of 
the inner and cutting side of the tooth, (Fig. 1, 
B. D.), whilst, on the outer side, a similar 
edge descended, but to a short distance from the 
point (Fig. 1, B. to C), and the convex portion 
of the tooth (A.) 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 sides, (as represented in the transverse 
section, Fig. 4, A. D). 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 (C), 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 curva- 
ture of the full-grown teeth, enabled them to 
retain, like barbs, the prey which they had 
penetrated. In these adaptations, we see con- 
trivances, which human ingenuity has also 
adopted, in the preparation of various instru- 
ments of art. 
In a former chapter (Ch. XIII.) I endea- 
