Note on some of the Generic Modifications of the Plesiosaurian Pectoral Arch

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Abstract
If not having a sternum the Plesiosauria differ from the Crocodilia and from all the Lacertian orders of Reptiles. Serpents with limbs being as yet undiscovered, the only true Reptilia which admit of comparison with Plesiosaurs in the pectoral bones are the Chelonians. And even here, at first sight, the resemblance is not so evident as to command attention; for the shapes of the plastron-bones in embryonic Tortoises are more suggestive of the pectoral and pelvic girdles of Plesiosaurians than are the internal chelonian bones which support the limbs, since in Plesiosaurs these osteological elements are expanded shields which cover much of the abdominal surface. When, however, the embryonic pectoral arch of such a Chelonian as the Chelone mydas (fig. 1) is critically looked at, only unimportant osteological modification is needed to change its characters to those of a Plesiosaur. The chelonian coracoid bones ( c ) are rod-like; but their extension is entirely posterior to the articulation for the numeric: the bones approximate somewhat posteriorly, are somewhat concave on their outer margin, and terminate in cartilages of a shoe-shaped form, which are so extended inward that their toe-like terminations meet in the median line. Then, from the humeral articulation the two precoracoids ( pc ) extend inward towards the median line; they are inclined very slightly forward, and join either by their cartilages or intervening connective tissue. If, now, a line be drawn to join the median points of meeting of

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