DINOSAUBIA 267 



width of these grooves varies in different teeth ; sometimes a 

 fourth small longitudinal ridge is developed on the ridged side 

 of the crown. The marginal serrations which, at first sight, 

 appear to be simple notches, as in the Iguana, present under 

 a low magnifying power (fig. 78), the form of -,,--.> 



transverse ridges, themselves notched, so as to ; . jji 



resemble the mammilated margins of the unworn 

 plates of the elephant's grinder ; slight groove- 

 lead from the interspaces of these notches upon 

 the sides of the marginal ridges. These ridges p io . 78 

 or dentations do not extend beyond the expanded Marginal ridges 

 part of the crown; the longitudinal ridges are f the Iguano- 

 continued farther down, especially the median ' ma S n - 



ones, which do not subside till the fang of the tooth begins to 

 assume its subcylindrical form. The tooth at first increases 

 both in breadth and thickness ; then it diminishes in breadth, 

 but its thickness goes on increasing ; in the larger and fully 

 formed teeth, the fang decreases in every diameter, and some- 

 times tapers almost to a point. The smooth unbroken surface 

 of such fangs indicates that they did not adhere to the inner 

 side of the maxillae, as in the Iguana, but were placed in 

 separate alveoli, as in the Crocodile and Megalosaur ; such 

 support w T ould appear, indeed, to be indispensable to teeth so 

 worn by mastication as those of the Iguanodon. 



The apex of the tooth soon begins to be worn away, and it 

 would appear, by many specimens, that the teeth were retained 

 until nearly the whole of the crown had yielded to the daily 

 abrasion. In these teeth, however, the deep excavation of the 

 remaining fang plainly bespeaks the progress of the successional 

 tooth prepared to supply the place of the worn-out grinder. 

 At the earlier stages of abrasion a sharp edge is maintained at 

 the ridged part of the tooth by means of the enamel which 

 covers that surface of the crown ; the prominent ridges upon 

 that surface give a sinuous contour to the middle of the cutting 



