244 GIGANTIC TERRESTRIAL SAURIANS. 
It has been stated, in the preceding section, 
that the large medullary cavities in the femur 
of the Iguanodon, and the form of the bones of 
the feet, show that this animal, like the Megalo- 
saurus, was constructed to move on land. 
A further analogy between the extinct fossil 
and the recent Iguana is offered by the presence 
in both of a horn of bone upon the nose, (PI. 24, 
Fig. 14). The concurrence of peculiarities so 
remarkable as the union of this nasal horn with 
a mode of dentition of which there is no ex- 
ample, except in the Iguanas, affords one of 
the many proofs of the universality of the laws 
of co-existence, which prevailed no less con- 
stantly throughout the extinct genera and spe- 
cies of the fossil w^orld, than they do among the 
living members of the animal kingdom. 
Feet. 
Length from snout to the extremity of the tail. ... 70 
Length of tail 52 J 
Circumference of body 14^ 
Mr. Mantell calculates the femur of the Iguanodon to be twenty 
times the size of that of a modern Iguana; but as animals do 
not increase in length in the same ratio as in bulk, it does not 
follow that the Iguanodon attained the enormous length of one 
hundred feet, although it approached perhaps nearly to seventy 
feet. 
As the Iguanodon, from its enormous bulk, must have been 
unable to mount on trees, it could not have applied its tail to the 
same purpose as the Iguana, to assist in climbing ; and the lon- 
gitudinal diameter of its caudal vertebrae is much less in propor- 
tion than in the Iguana, and shows the entire tail to have been 
comparatively shorter. 
