OF CREATION. 211 



trivance being the formation of a slant surface of 

 the crown of the tooth, and therefore of a sharp 

 cutting edge. While young, the tooth presents a 

 sharp cutting edge, and is lancet-shaped (81) : as 

 it grows further out from the jaw, it assumes the 

 form seen in fig. 80, and is then a powerful in- 

 strument, well adapted to separate tough vegetable 

 fibre ; while in its most advanced state (79) it 

 ceases to be adapted to this purpose, but is strong 

 and flat, and at the same time uneven, the pulp of 

 the tooth projecting from the surface, which is worn 

 so as to be nearly horizontal, and forming a trans- 

 verse ridge. The teeth therefore begin by being 

 incisors, and, in the course of time, as they become 

 worn, they pass into the condition of grinders, a cu- 

 rious change, providing for the animal a perpetual 

 supply of teeth of all kinds, some enabling it to nip 

 off tough vegetable food, and others helping to grind 

 that food properly before it is committed to the 

 stomach. 



The vertebral column of the Iguanodon is on a 

 scale commensurate with the vast bulk of the animal. 

 The vertebrae themselves have nearly flat surfaces, 

 and are large and somewhat wedge-shaped, exhibit- 

 ing rather crocodilian than lacertian analogies, al- 

 though essentially different from both those types of 

 structure. The neck is not known, since no vertebrae 

 have yet been found belonging to this part. The sacrum, 

 or that part of the back-bone cemented together to 

 distribute the weight of the body on the hinder extre- 

 mities, includes five vertebrae, as in the megalosaur ; 

 and in one specimen this continuous solid ridge of bone 

 measures seventeen inches in length, and its breadth, 



