Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/167

 Rh

This hypothesis of Cuvier is but conjectural, respecting the power of the Plesiosaurus to change the colour of its skin; and to the inexperienced in comparative anatomy, it may seem equally conjectural, to deduce any other conclusions respecting such perishable organs as the lungs, from the discovery of peculiar contrivances, and unusual apparatus in the ribs; yet we argue on similar grounds, when from the form and capabilities of these fossil ribs, we infer that they were connected, as in the Chameleon, with vast and unusual powers of expansion and contraction in the lungs; and when, on finding the ribs and wood-work of a worn-out bellows, near the ruins of a blacksmith's forge, we conclude that these more enduring parts of the frame of this instrument, have been connected, with a proportion able expansion of leather.

The compound character of the ribs, probably also gave to the, Plesiosaurus the same power of compressing air within its lungs, and in that state taking it to the bottom, which we have considered as resulting from the structure of the sterno-costal apparatus of the Ichthyosauri.

As the Plesiosaurus breathed air, and was therefore obliged to rise often to the surface for inspiration, this necessity was met by an apparatus in the chest and pelvis, and in the bones of the arms and legs, enabling it to ascend and descend in the water after the manner of the Ichthyosauri and Cetacea; accordingly the legs were converted into paddles, longer and more powerful than those of the Ichthyosaurus, thus compensating for the comparatively small assistance which it could have derived from its tail.