MEGALOSAURUS. 181 



in the same quarries, that we are nearly as well acquainted 

 with the form and dimensions of its limbs, as if they had 

 been found together in a single block of stone. 



From the size and proportions of these bones, as com- 

 pared with existing Lizards, Cuvier concludes the Megalo- 

 saurus to have been an enormous reptile, measuring from 

 forty to fifty feet in length, and partaking of the structure of 

 the Crocodile and Monitor. 



As the femur and tibia measure nearly three feet each, 

 the entire hind-leg must have attained a length of nearly 

 two yards : a metatarsal bone, thirteen inches long, indi- 

 cates a corresponding length in the foot.* The bones of 

 the thigh and leg are not solid at the centre, as in Croco- 

 diles, and other aquatic quadrupeds, but have large medul- 

 lary cavities, like the bones of terrestrial animals. We learn 

 from this circumstance, added to the character of the foot, 

 that the Megalosaurus Hved chiefly upon the land. 



In the internal condition of these fossil bones, we see the 

 same adaptation of the skeleton to its proper clement, which 

 now distinguishes the bones of terrestrial, from those of 

 aquatic Saurians.f In the Ichthyosauri and Plesiosauri, 

 whose paddles were calculated exclusively to move in 

 water, even the largest bones of the arms and legs were 

 solid throughout. Their weight would in no way have 

 embarrassed their action in the fluid medium they inhabited; 

 but in the huge Megalosaurus, and stiU more gigantic 

 Iguanodon, which are shown by the character of their feet 

 to have been fitted to move on land, the larger bones of the 

 legs were diminished in weight, by being internally hollow, 

 and having their cavities filled with the light material of 



1826, saw fragments of a jaw, containing teeth, and of some other bones 

 of Megalosaurus, in the museum at Bcsangon, from the oolite of that neigh- 

 bourhood. 



• See Geo). Trans. 2d series, Vol. 3, p. 437, PI. 41. 



t I learn from Mr. Owen that the long bones of land Tortoises have a 

 close cancellous internal structure, but not a medullary cavity. 



VOL. I. 16 



