176 



THE OSTEOLOGY OF THE REPTILES 



The carpus in the Dinosauria (Fig. 141) has suffered greater reduc- 

 tion 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, 



Fig. 1 42. Pterosaur limbs: A, Pterodactylus. American Museum of Natural History. Nearly 

 three times natural size. B, Rhamphorhynchus. After Plieninger. One half natural size. 



ulnare, and pisiform ; perhaps that was also the case in the Sauropoda 

 (Fig. 141 r). A small bone may possibly represent a vestigial inter- 

 medium 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 alHes of the Theropoda. The carpus 

 in the Trachodontidae (Fig. 141 h) is more reduced than in any other 



