Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/95

 AND AYES OF NORTH AMERICA. 89 posterior to its position in ordinary reptilia. This, taken in connection with the anterior position of the support of the body the femur, rendered the erect progress of the Dino-sa aria possible. Another approximation to the birds \\ill probably be found in the sternum and coracoids. These elements arc but little known, and that imperfectly ; the best example has been furnished by the great Teratosaurus suevicus Mey. Here, according to Plienin-ger, the elements corresponding to the xiphisternum of Lacertilia is a large thin shield-like bone, of elongate form. The corticoids are narrow, prismatic bones; and abut against the anterior angles of the xiphisternum ; being entirely different from the broad fiat element of the Lacertilia and other orders, which are usually extensively in contact with each other or with the xiphisternum. We have, hove; er, among Dinosauria, as among Quadrumanous Mammalia, a series of forms, from those constantly assuming the prone Lacertian position, to those that walked exclusively erect like birds. Perhaps the most Lacertilian fonn known is the genus Scelidosaurus of Owen : the greater equality in length of the limbs, and the numerous toes, as well as lacertilian dentition assign it to this place. Then we find forms like Iguanodon and Hadrosaurus, the most gigantic of land animals, where a semi-erect atti-tude was the natural one, as they like the Megatherium and Megalonyx lived on vegeta-ble food, and were necessitated to raise themselves on their hinder limbs to reach it. Here the bird-like type is approached, in the ieduction of the metatarsi to three, and the great antero-posterior extent of the ilium. In the genus Laelaps the position was probably quite, erect, and additional resemblances to the ornithic type are adapted to large animals no longer requiring a vegetable diet, but procuring their living food by activity and strength. They are accordingly organized so as to be entirely independent of extraneous support, and furnished with great powers either of running or leaping. Intermediate between this extreme, and the type of Iguanodon, comes a. large carniv-orous genus, the INIegalosaurus of Buckland, the representative of types like Laelaps, in the old world. In its longer fore limbs it differs from the most bird-like forms. A car-nivorous type only known from teeth, is Aublysodon Leidy ; it is American. The other herbivorous species, of less size than Iguanodon, which was furnished with a dorsal series of dermal bones, is the Hylaeosaurns armatus Mantell, found in the Wealden of England; while an allied form which was covered with long massive deimal spines, has recently been discovered in the same formation in the Isle of Wight, and referred to the genus Polyacanthus Owen. The sizes of the best known species of these genera are as follows : AMERI. Pi3ILOSO. SOC.-VOL. XIV. 23