2G6 



I \l i. ONTOLOGY 



gating dental structure, the actual amount of correspondence 

 between the Iguanodon and Iguana in this respect. This has 

 been done in the author's general description of the teeth of 

 reptiles,* from which the following notice is abridged : — The 

 teeth of the Iguanodon (fig. 77), though resembling most 



closely those of 

 the Iguana, do not 

 present an exact 

 magnified image of 

 them, but differ in 

 the greater relative 

 thickness of the 

 crown, its more com- 

 plicated external 

 surface, and, still 

 more essentially, in 

 a modification of the 

 internal structure, 

 by which the Igua- 

 nodon equally deviates from every other known reptile. 



As in the Iguana, the base of the tooth is elongated and 

 contracted ; the crown expanded and smoothly convex on the 

 inner side ; when first formed it is acuminated, compressed, 

 its sloping sides serrated, and one surface, external in the 

 upper jaw, internal in the lower jaw, is traversed by a median 

 longitudinal ridge, and coated by a layer of enamel ; but 

 beyond this point the description of the tooth of the Igua- 

 nodon indicates characters peculiar to that genus. In mosl 

 of the teeth that have hitherto been found, three longitudinal 

 ridges traverse the ridged surface of the crown, one on each 

 side of the median primitive ridge ; these are separated from 

 each other and from the serrated margins of the crown by 

 four vide and smooth Longitudinal grooves. The relative 



* Odontography, pt. ii., p. 249; Transactions of the Hou-ii A^oeiation. is:ss. 



Front and side views of a tooth of the lower jaw of 

 the Iguanodon, nat. size. 



