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The ribs are composed of two parts, one vertebral and one ventral; the ventral portions of one side, (Pl. 18, 3, b,) uniting with those on the opposite side by an intermediate transverse bone, (a, c,) so that each pair of ribs encircled the body with a complete belt, made up of five parts. Cuvier observes that the similarity of this structure to that of the ribs of Chameleons and two species of Iguana, (Lacerta Marmorata, Lin. and Anolius, Cuvier,) seems to show that the lungs of the Plesiosaurus Dolichodeirus, (as in these three subgenera of living Saurians,) were very large; and possibly that the colour of its skin also was changeable, by the varied intensity of its inspirations. Oss. Foss. Vol. V. Pt. 2. p. 280.