Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/145

 Rh constructed after the manner of fishes, had they been furnished with legs instead of paddles, could not have moved on land without injury to their backs.

The ribs were slender, and most of them bifurcated at the top: they were also continuous along the whole vertebral column, from the head to the pelvis, (see Plates 7, 8, 9); and in this respect agree with the structure of modern Lizards. A considerable number of them were united in front across the chest: their mode of articulation may be seen in Pl. 14. The ribs of the right side were united to those of the left, by intermediate bones, analogous to the cartilaginous intermediate and sternal portions of the ribs in Crocodiles; and to the bones which, in the Plesiosaurus, form what Mr. Conybeare has called the sterno-costal arcs. (See Pl. 17.) This structure was probably subservient to the purpose of introducing to their bodies an unusual quantity of air; the animal by this means being enabled to remain long beneath the water, without rising to the surface for the purpose of breathing.