DINOSAUKIA. 297 



required as a triturating instrument. The enamel covers 

 only the harder dentine, forming the ridged side of the 

 tooth. The adaptation of this admirable dental instrument 

 to the cropping and comminution of such tough vegetable 

 food as the Clathrarim and similar plants, which are found 

 buried with the Iguanodon, is pointed out by Dr. Bucklancl, 

 with his usual felicity of illustration, in his Bridgewater 

 Treatise, vol. i., p. 246. 



But the microscopical examination of the structure of the 

 Iguanodon* s teeth has contributed additional evidence of the 

 perfection of their adaptation to the offices to which their 

 more obvious characters had indicated them to have been 

 destined. 



To preserve a trenchant edge, a partial coating of enamel 

 is applied ; and, that the thick body of the tooth might be 

 worn away in a more regularly oblique plane, the dentine is 

 rendered softer as it recedes from the enamelled edge, by the 

 simple contrivance of arresting the calcifying process along 

 certain tracts of the opposite wall of the tooth. When attri- 

 tion has at length exhausted the enamel, and the tooth is 

 limited to its function as a grinder, a third substance has been 

 prepared in the ossified remnant of the pulp to add to the 

 efficiency of the dental instrument in its final capacity. And 

 if the following reflections were natural and just, after a re- 

 view of the external characters of the dental organs of the 

 Iguanodon, their truth and beauty become still more manifest 

 as our knowledge of their subject becomes more particular 

 and exact : — 



" In this curious piece of animal mechanism we find a 

 varied adjustment of all parts and proportions of the tooth to 

 the exercise of peculiar functions, attended by compensations 

 adapted to shifting conditions of the instrument during dif- 

 ferent stages of its consumption. And we must estimate the 

 works of nature by a different standard from that which we 



