MEGALOSAURUS. 
235 
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 corres- 
ponding 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, 
've see the same adaptation of the skeleton to 
Its proper element, which now distinguishes the 
bones of terrestrial, from those of aquatic Sau- 
nans.t 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 vsmuld 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 
* See Geol. Trans. 2nd series, Vol. 3, p. 427, PI. 41. 
t I learn from Mr. Owen that the long bones of land Tor- 
oises have a close cancellous internal structure, but not a me- 
dullary cavity. 
