THE POSE AND LOCOMOTION OF DIPLODOCUS 3 



the hind foot of the elephant; but, to judge from various mounted 

 skeletons and from good figures of others, one can hardly suppose that 

 the heel of the elephant is lifted farther from the ground relatively 

 than that of the tortoise. 



I grant that Dr. Abel's efforts are along a line where they are needed. 

 Those who believe in the mammal-like gait of Diplodocus ought to 

 give their reasons therefor. I do not assert that reasonable argu- 

 ments for their view cannot be produced, but hitherto the correctness 

 of this view has been assumed. The subject is a difficult one and 

 needs to be studied from various points of view and by all who have 

 the opportunity. And in studying the movements of animals one 

 soon learns that they can assume so many positions that one may be 

 at loss, in the case of an extinct creature, to determine which positions 

 were the usual ones. 



In the primitive condition the limbs of the Tetrapoda stand out 

 at right angles with the body,- and in approximately this position they 

 are found in most Amphibia and Reptilia. When these animals are 

 walking, the humerus and the femur move backward and forward 

 mostly in horizontal planes. In most mammals, on the contrary, 

 the humerus is turned backward against the thorax and the femur 

 forward against the flank. The hand, which otherwise would be 

 directed backward, is turned forward by the crossing of the bones of 

 the lower arm. The movements of arm and leg are then mostly in 

 sagittal planes. In the duckbill and the echidnas the limbs have 

 retained the position found in most reptiles. 



Now, among all the reptiles that live today there are none, except 

 perhaps the chameleons, that have attained even an approach to the 

 condition found among the mammals. 



It is evident that before the close of the Jurassic there existed both 

 carnivorous and herbivorous dinosaurs that went about habitually 

 on only their hinder legs; but it is by no means necessary to believe 

 that the immediate ancestors of these bipeds walked first like mammals 

 and afterwards like birds. It is well known that certain lizards can 

 run swiftly on their hind legs, the fore legs and the tail being held 

 free from the ground. Furthermore, as may be seen from W. Saville- 



' Huxley, Anat. Vert. Animals, 1872, p. T,y, Flower's Osteology of the 

 Mammalia, 1885, p. 362. 



