Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/144

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The vertebral column in the Ichthyosaurus was composed of more than one hundred joints; and although united to a head nearly resembling that of a Lizard, assumed, in the leading principles of its construction, the character of the vertebræ of fishes. As this animal was constructed for rapid motion through the sea, the mechanism of hollow vertebræ, which gives facility of movement in water to fishes, was better calculated for its functions than the solid vertebra of Lizards and Crocodiles (See Plate 12, A. and B.) This hollow conical form would be inapplicable to the vertebrae of land quadrupeds, whose back, being nearly at right angles to the legs, requires a succession of broad and nearly iiat qrfaces, which press with considerable weight against each other. It is quite certain, therefore, that such large and bulky creatures as the Ichthyosauri, having their vertebræ

tion of weight or bulk; a similar structure may be noticed in the overlapping bones of the heads of fish, and in a less degree, in those of Turtles.—Geol. Trans. Lond. Vol. V. p. 565, and Vol. I. N. S. p. 112.