426 



THE WONDERS OF GEOLOGY. Lect. IV. 



The deciduous tooth of an adult Iguanodon, with the crown flat, 

 and the fang absorbed, is well exemplified in this specimen (Lign. 

 1 04) from the Isle of Wight ; in which the crown is worn down almost 

 to the neck ; the series of denticulated plates having entirely disap- 

 peared. In this respect the Iguanodon differs from all known living 

 or extinct lizards ; for all other herbivorous 

 reptiles chip off and swallow their food whole ; 

 the construction of their jaws not admitting 

 of a grinding motion. It is therefore obvious, 

 not only that the Iguanodon fed on vegetables, 

 but that it was capable of masticating its 

 food like the horse and other herbivorous 

 mammalia : while the absorption of the fang 

 shows that a constant succession of teeth took 

 place at all periods of the animal's existence, 

 as is the case in many other reptiles. The 

 tooth, when examined microscopically, exhibits 

 a corresponding internal structure ; the tooth- 

 ivory or dentine being of a softer and coarser 

 texture than in other reptiles, and resembling 

 that of the great vegetable feeders of the sloth 

 Lign. 104.— Tooth of an tribe (ante, p. 167).* These dental instruments 

 Iguanodon; from Brook must therefore have been admirably adapted, in 

 Bay, isle of Wight. (Nat. everv stage, for the laceration and comminution 

 of the tough vegetable substances, which there 

 can be no doubt constituted the chief food of this colossal quadruped. 



A portion of the lower jaw of a young Iguanodon, with 

 the fangs of fifteen teeth, closely and evenly set, in a regu- 

 lar series, and imbedded laterally in grooves of the dentary 

 bone, and with germs of successional teeth at the base of 

 the old one, indicate a close analogy to the arrangement of 

 the teeth in the recent Iguana, but with this difference, 

 that in the living kind there are no sockets ; the teeth 

 being attached laterally to a parapet of the dental bone ; 

 while, in the Iguanodon, the smooth surface and pointed 

 termination of some of the fangs, indicate an implantation 

 in distinct alveoli. f 



* Medals of Creation, vol. i. 1M. VI. //>/. 4. 



f Philosophical Transactions for 1841. PI. V. fig. 1 ; and PL VII. 

 figs. 1,2; p. 131. 



