134 
DR. MANTELL ON A PORTION OF THE LOWER JAW 
the purpose of seizing food. The herbivorous reptiles gnaw off the vegetable produc- 
tions on which they feed, but do not chew them. This character is so constant, that 
the discrepancy presented by the teeth of the Iguanodon, led even Baron Cuvier at 
first to suppose that they belonged to a Mammifer. “ Ce qui leur donne un caractkre 
unique, c’est d’user leurs points transversalement comme les quadrupedes herbivores, 
et tellement que la premiere qui me fut presentee s’etant trouvee dans cet etat de 
detrition je ne doutai nulleinent qu’elle ne vint d’un Mammifere ; il me sembloit meme 
qu’elle ressembloit beaucoup a une macheliere de rhinoceros. Ce n’est que depuis 
que M. Mantell m’en a envoye une serie d’entieres et de plus ou moins usees que je 
me suis enti&rement convain^u de mon erreur*.” In the Iguana, the teeth that have 
been much used present a chipped or fractured appearance, as if the points had been 
broken or splintered off; in the Iguanodon, on the contrary (as seen in Plate VI. figs. 
1. 5. 6.), the most perfect teeth have a ground and even surface at the summit of the 
crown ; for it is not correct (as some have surmised), that in any stage they acted as 
pincers or wire-nippers, nor do any of the specimens possess “ cutting edges with 
points of enlargement and contraction.” The enamel is traversed by numerous un- 
dulated transverse lines, but these have been produced by the mode of growth ; and 
the worn margin of enamel that borders the crown of the tooth invariably exhibits a 
smooth entire edge. The Iguanodon, therefore, must have been furnished with 
powerful maxillary muscles, to enable it to effect the trituration of the hard and tough 
vegetable substances, which, from the worn condition of the teeth, we are warranted 
in assuming to have been its food ; and the articular, surangular, and complementary 
bones of the lower jaw, must have been developed accordingly, to have given attach- 
ment and support to the muscular apparatus by which mastication was effected. The 
external surface of the small portion of the dentary bone in the specimen (see Plate V. 
fig. 8.), appears to indicate the attachment of powerful muscles ; it is very different 
from the smooth corresponding part in the Iguana. The discovery of the entire jaw, 
or of some part of its articular extremity, will therefore be fraught with great in- 
terest. 
The number of teeth in the fossil, in a space equal in length to the width of the 
jaw at the operculo-dental suture, is eight ; in the Iguana the corresponding space 
would be occupied by six teeth. The same admeasurement in the Iguana is equal 
to one-fourteenth of the length of the jaw; and if in the fossil animal the same 
relative proportions were maintained in other parts of the skeleton, the length of the 
jaw would be ten inches and a half, and of the entire reptile about fourteen feet, which 
is scarcely equal to one-seventh of the magnitude which some individuals must have 
attained. Of course these calculations can only be considered as approximative^. 
* Cuvier, Oss. Foss., tom. v. p. 351. 
t Some years since I discovered in the same quarry a fragment of bone, seven inches long, which appears to 
be a portion of the alveolar plate of the lower jaw of a gigantic Iguanodon, but it is too imperfect to admit of 
accurate determination. It is placed in the British Museum with the specimen above described. 
