Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/92

 86, THE EXTINCT BATRACHIA7 REPTILIA 3D I 1\T 0 S.A.T_T Ft _ The ilium extended horizontally forwards, and supporting a number of vertebrae anterior to the two saerals of other Iteptilia. A.cetabulum perforate, and partly en-dosed peripherally by the ilium and pubis. Pubes elongate, parallel ; isehia longitudinal, in plane of ilium, elongate, with distinct head for pubis. Femur with transverse neck and head, and third troehauter. " Cervical and anterior dorsal vertebrfc with pat and diapo-physes, for articulation with bifurcate ribs." Neural arches of dorsal lertebrie attached by suture ; of saerals, shifted over the intervertebral sutures. The structures presented by the Dinosauria have presented greater difficulty of expla-nation than any other type of extinct vertebrates.* This has in part iesulted from the attempt so assign them to types already known, and to explain their structures in accoid-ance therewith ; a course scarcely consistent with our present knowledge of the peculiari-ties of the parts themselves. The type is a good illustration of the necessity of interpreting extinct forms by a combination of the " law of successional relation," with " the law of types " or of morphological " eorrellation," and not by either alone. The direction assigned to pubes in this order, is suggested by considerations explained below They have probably diverged forwards and downwards from the vertebral column and their great length indicates a prominent abdomen.. The only Dinosaurs where they are preserved in place, the Stenopelix valcleiisis of Von Meyer, and Compsognathus longipes of 'Wagner, justify this proposition. The ischium in Stenopelix and Teratosaurus is a broad flattened bone slightly curved in the lateral direction, and of sufficient strength with its fellow, to support the weight of the animal when in a sitting posture. The pubes in Hadrosaurus and Compsognathus are much more slender and proximally dilated ; as in the Crocodiles the chief support of each is derived from the articulation with an anterior tuberosity of the ischium. The articulation with the isehium is probably wanting or very slight and ligamentous, and the acetabuluin was thus open, a large foramen being included by the three bones which usually compose it. The head of the femur is trans\ erse to the direction of motion of the condyles, and not oblique as in modern lizards. Henee the motion of this element was in a line paral-lel with the axis of the body, and the limb could not be directed obliquely from that axis so as to allow the body to lest on the ground between them in the ordinary progression of the animal, as is the ease with Iguanas, Crocodiles, etc. The fore limbs appear to have been weak, even when somewhat elongate, as in Iguanodon. Their articulation with the scapula is a singular part of the structure. In
 * For discussions of these relations see Proceed. Ac, Nat. Sci., Phila., 1866, 317, and Proceed. Amer. Philos. Soc., 1869, 16.