No. 52.-)] THE SAUEOPODOUS DINOSAURS 



519 



lizards walk or run in this way at times. He does not 

 deny that even the Sauropoda may have done so at times, 

 but regards them as too massive and heavy for this to 

 have been their normal mode of progress. But his chief 

 protest is again-t the placing of the knee and elbow joints 

 in sagittal planes (i. <?., bending parallel with the middle 

 line of the body) as in mammals, instead of bending out- 

 ward as in all modern reptiles. In certain points of his 

 argument he makes out a convincing case in the re- 

 viewer's opinion; other points may be satisfactorily 

 answered. 



Dr. Hay misstates the supposed significance of the 

 peculiar type of femur seen in Diplodocus. He observes : 



But no one, so far as the reviewer knows, has asserted 

 that the straightness of the shaft of the femur of Diplo- 

 docus, considered alone, proved that the animal walked 

 like a mammal. For among mammals there are both 

 straight and curved femora, and a wide variety of gaits. 



The argument that Dr. Hay presumably has in mind 

 is this: That in the elephants and several other types of 

 gigantic mammals the femur is relatively long, straight- 

 shafted, with its articulations terminal rather than lat- 

 eral, the feet short, rounded, heavily padded and capable 

 of but limited motion, the whole limb being pillar-like and 

 normally held straight under the body. All gigantic 

 mammals show some degree of approach towards this 

 type of limb; and in the Sauropoda the resemblance in 

 form and proportions is very marked. The same type is 

 seen in Coryphodon, Uintatherium, Titanotherium, 

 Arsinoitherium, Pyrotherium, Astrapotherium, Dipro- 



