IGUANODON. 187 



similar, if not a still warmer climate, prevailed at the time 

 when so huge a Lizard as the Iguanodon inhabited what are 

 now the temperate regions of the southern coasts of England. 

 We know from the fragment of a femur, in the collection 

 of Mr. Mantell, that the thigh-bone of this reptile much ex- 

 ceeded in bulk that of the largest Elephant: this fragment 

 presents a circumference of twenty-two inches in its small- 

 est part, and the entire length must have been between four 

 and five feet. Comparing the proportions of this monstrous 

 bone with those of the fossil teeth with which it is associated, 

 it appears that they bear to one another nearly the same 

 ratio that the femur of the Iguana bears to the similarly 

 constructed and pecuhar teeth of that animal.* 



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 

 Megalosaurus, was constructed to move on land. 



A farther analogy between the extinct fossil and the re- 

 cent Iguana is offered by the presence in both of a horn of 



* From a careful coniparisioii of llic bones of the Iguanodon with those of 

 the Iguana, made by taking an average from the proportions of different 

 bones from eight separate parts of the respective skeletons, Mr. Mantell 

 has arrived at these dimensions as being the proportionate measures of the 

 following parts of this extraordinary reptile : 



Feet. 



Length from snout to tiic extremity of the tail • . 70 



Length of tail -----.--. 52^ 



Cireumference of body .--..-. 14^ 



Mr. Mantel! ealeulates the femur of tiie Iguanodon to be twenty times the 



size of that of a modern Iguana ; but a.; animals do not increase in length 



in the same ratio as in bulk, it do(^s 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 ennrni;.U3 bulk, must have been unable to 

 mount on trees, it could not have ajip'ied iis tail to the same purpose as the 

 Iguana, to assist in clinibing; and ilie longitudinal diameter of its caudal 

 vertebrce is much less in proportion fhan in the Ignana, and shows the en- 

 tiro tail to have been comparatively shorter. 



