Fig. 142. Pterosaur limbs: A, Pterodactylus. American Museum of Natural History. Nearly three times natural size. B, Rhamphorhynchus. After Plieninger. One half natural size.
The carpus in the Dinosauria (Fig. 141) has suffered greater reduction than in any other order of terrestrial reptiles, doubtless because of the upright posture. In no form has a centrale been reported, and the fifth carpale is doubtfully present in any (Camptosaurus), as would be expected from the constantly reduced fifth finger. In the quadrupedal forms there are but two proximal bones, both large and massive. In Stegosaurus (Fig. 141 i, j) the postaxial one of the two has been found in young specimens in three parts, the intermedium, ulnare, and pisiform; perhaps that was also the case in the Sauropoda (Fig. 141 f). A small bone may possibly represent a vestigial intermedium in Leptoceratops (Fig. 141 m) of the Ceratopsia. In the Theropoda, and iguanodont orthopods, that is, bipedal forms, the radiale, intermedium, and ulnare seem distinct in all, though not large. The second row of carpals has disappeared in the Sauropoda (Fig. 141 f) and Stegosauria (Fig. 141 i). Two have been found in all other known forms, except the Trachodontidae; in most cases the third and fourth carpale, though identified as the first and second in Ornitholestes and its immediate allies of the Theropoda. The carpus in the Trachodontidae (Fig. 141 h) is more reduced than in any other
