DR. MANTELL ON THE IGUANODON. 
197 
sent the very counterpart of that of the Iguanodon. This striking resemblance will 
be obvious to any one who will compare the illustrations subjoined to this memoir, 
with the magnificent specimen of the Mylodnn rohustiis in the Hunterian Museum*. 
The great size and number of the vascular foramina distributed along the outer side 
of the dentary bone and beneath the border of the symphysis (Plate XVI. fig. 2, and 
Plate XVII. fig. 4), 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 develop- 
ment of the integuments and soft parts with which the lower jaw was invested •f-. 
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 pro- 
duced, and capable of being protruded and retracted, so as to constitute in conjunc- 
tion with a large fleshy prehensile tongue, a powerful instrument for seizing and 
cropping the leaves and branches, which, from the construction of the teeth, we may 
infer constituted the chief food of the Iguanodon. 
Thus we find the mechanism of the maxillary organs of the Wealden herbivorous 
Saurian, as elucidated by recent discoveries, in perfect harmony with the remarkable 
dental characters which rendered the first known teeth so enigmatical to the palae- 
ontologist, and another interesting proof is obtained of the constancy of those laws 
by which the correlation of organic structures is governed. 
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 slight and 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 herbivorous Eden- 
tata which flourished in South America, ages after the Country of the Iguanodon and 
its inhabitants had been swept from the face of the earth. 
Thus in the unlimited production of successional teeth at every period of the ani- 
mal’s existence, in the mode of implantation of the teeth, and in the composite struc- 
ture of the lower jaw — each ramus consisting of six distinct elements — the Saurian 
type of organization is unequivocally manifest ; while the intimate structure of the 
dental organs corresponds with that of the Sloths, and the subalternate arrangement 
and reversed position of the upper and lower series of teeth, with that of the Rumi- 
nants. And again, the edentulous and prolonged symphysis, and the great develop- 
* In tlie Mylodon T>arwimi the rami of the lower jaw anterior to the teeth are contracted vertically, and con- 
verge to a longer and narrower symphysis, which is inclined forwards at a more open angle with the horizontal 
ramus, than in the Mylodon robustus ; and therefore still more nearly approaches that of the Iguanodon. See 
Professor Owen on the Mylodon. 
t The external vascular foramina are remarkably augmented in the dentary bone of the Iguanodon as com- 
pared with other reptiles. In the colossal Mosasaurus, the dentary piece of a jaw 4^ feet long, has hut ten or 
twelve relatively small foramina ; in the Iguana hut five or six ; in the Monitors six ; in the Crocodiles they 
are numerous, but small and irregular. In the Megalosaurus there are four foramina, and several small ones. 
2 D 2 
