196 SUPPLEMENTAEY NOTES. 



discovery of the cranium, and of perfect examples of the upper and lower jaws with both 

 successional and mature molars in their natural position, may modify, but, we believe, will in no 

 material respect invalidate these conclusions. 



In instituting a comparison between the maxillary organs of the Iguanodon, and those of 

 the existing herbivorous lizards, we are at once struck with their remarkable deviation from all 

 known types in the class of reptiles. In the Ambhirhynchi (of the Galapagos Islands) , the most 

 exclusively vegetable feeders of the Saurian order, the alveolar process beset with teeth is 

 continued round the front of the mouth : the junction of the two rami of the lower jaw at the 

 symphysis presenting no edentulous interval whatever, the lips not being more produced than in 

 other reptiles ; but this creature only bruises its food ; it cannot grind or masticate it. In fact, 

 the edentulous, expanded, scoop-shaped, procumbent symphysis of the lower jaw of the 

 Iguanodon, has no parallel among either recent or fossil reptiles ; and we seek in vain for organs 

 at all analogous, except among the herbivorous mammalia. The nearest approach is to be found 

 in certain Edentata ; as for example in the Cholcepus didactylus, or Two-toed Sloth, in which the 

 anterior part of the lower jaw is destitute of teeth, and much prolonged. The correspondence is 

 still closer in the extinct gigantic Mylodons, in which the symphysis resembles the blade of a 

 turf-spade, and has no traces of incisor sockets ; and were not this part of the jaw elevated 

 vertically in front, and the two sides confluent, it would present the very counterpart of that of 

 the Iguanodon. The great number and size of the vascular foramina distributed along the outer 

 side of the dentary bone in the Wealden reptile, and the magnitude of the anterior outlets which 

 gave exit to the vessels and nerves that supplied the front of the mouth, indicate the great 

 development of the integuments and soft parts with which the lower jaw was invested. 



The sharp ridge bordering the deep groove of the symphysis, in which there are also several 

 foramina, evidently gave attachment to the muscles and integuments of the under lip ; and there 

 are strong reasons for supposing that the latter was greatly produced, and capable of being 

 protruded and retracted so as to constitute, in conjunction with a long extensile tongue, a suitable 

 instrument for seizing and cropping leaves and branches, which, from the construction of the 

 teeth, we may infer was the food of the Iguanodon. 



Thus we find the mechanism of the maxillary organs of the "Wealden herbivorous saurian, 

 as demonstrated by recent discoveries, in perfect harmony with the remarkable dental characters 

 which rendered the first known teeth so enigmatical. In the Iguanodon we have a solution of 

 the problem, how the integrity of the type of organization peculiar to the class of cold-blooded 

 vertebrata was maintained, and yet adapted by simple modifications to fulfil the conditions 

 required by the economy of a gigantic terrestrial reptile, destined to obtain support exclusively 

 from vegetable substances ; in like manner as the extinct colossal sloth-like Edentata of South 

 America. In fine, we have in the Iguanodon the type of the terrestrial herbivora, which in that 

 remote epoch of the earth's physical history — the Age of Reptiles — occupied the same relative 

 station in the terrestrial fauna, and fulfilled the same general purposes in the economy of nature, 

 as the Mylodons, Mastodons, and Mammoths, of the tertiary periods, and the large pachyderms 

 of modern times. 



Although some important data are stiU required to complete our knowledge of the structure 

 of the Iguanodon, we are warranted in concluding that this colossal herbivorous reptile was as 

 bulky as the elephant, and as massive in its proportions : for, living exclusively on vegetable 

 substances, the abdominal region must have been largely developed. Its limbs must have been 

 of proportionate size to support and move so enormous a carcass. The hinder extremities 

 probably presented the unwieldly contour of those of the Hippopotamus, and were based on 



