254 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



situated in the latter. If this interpretation be correct, then 

 the upper and lower molars were related to each other nearly 



UPPER MOLARS. 



Outer aspect. Inner aspect. 



2 



LOWER MOLARS. 



LIGN 56. UPPER AND LOWER TEETH OF THE IGUANODON, IN THEIR 

 PRESUMED NATURAL ARRANGEMENT. 



(| not. size.) 



Fig. 1. Two upper molars, the crowns worn by use; the external aspect showing 



the ridged and enamelled face. 

 2. Inner aspect of the same. 

 3. A mature lower molar ; the external aspect; exposing the two oblique facets 



worn by friction against the pair of upper teeth. 

 4. Inner aspect of a lower molar, displaying the longitudinal ridges, and 



serrated edges ; a coronal germ of a successional tooth is seen in a cavity 



at the base of the fang. 



as in the Ruminants ; the outer aspect below corresponding 

 to the inner above ; the triturating facet inclining from above 

 downwards and outwards in the inferior series, and from below 

 upwards and inwards in the superior; in the lower teeth the 

 enamelled edge is within and the most elevated, while in the 

 upper it is external and the lowest. 



By this adjustment the harder dentine with its coating of 

 enamel, played on the softer vaso-dentinal tract of the tooth 

 opposed to it below ; and a bevelled or chisel-like surface was 

 maintained for triturating the food when drawn into the 



