Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/185

 Rh 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 compared with existing Lizards, Cuvier concludes the Megalosaurus 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, indicates a corresponding length in the foot. The bones of the thigh and leg are not solid at the centre, as in Crocodiles, and other aquatic quadrupeds, but have large medullary cavities, like the bones of terrestrial animals. We learn from this circumstance, added to the character of the foot, that the Megalosaurus lived chiefly upon the land.

In the internal condition of these fossil bones, we see the same adaptation of the skeleton to its proper element, which now distinguishes the bones of terrestrial, from those of aquatic Saurians. 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 still 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 strata. The author, in 1826, saw fragments of a jaw, containing teeth, and of some other bones of Megalosaurus, in the museum at Besançon, from the oolite of that neighbourhood.