Fig. 437. (A) Skeleton of Seymour ia, in dorsal view; original about 20 inches 

 long. It is uncertain whether Seymouria should be regarded as a very primitive 

 reptile (a cotylosaur) or as a somewhat reptilian amphibian. (After Williston.) 

 (B) Skeleton of the Lower Triassic cynodont Cynognathus. (After Gregory and 

 Camp.) (Courtesy, Romer: "Vertebrate Paleontology," Chicago, University of 

 Chicago Press.) 



Fig. 438. {Left) Alligator. (Right) Australian dog, dingo. In most lower tetra- 

 pods the short legs sprawl and the animal crawls. In most mammals the longer legs. 

 with elbow-bend pointing backward and knee-bend pointing forward, are adapted 

 for speed and agility. (Left, courtesy, Ditmars: "The Reptile Book," New York, 

 Doubleday & Co., Inc. Right, courtesy, Museum of Comparative Zoology, Harvard 

 University.) 



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