678 



THE AMERICAN NATURALIST 



[Vol. XLII 



The current conception is one that is easily accounted for. 

 Before exact knowledge of these reptiles had been gained, 

 it was known that the dinosaurs of the other groups, 

 herbivorous and carnivorous, walked erect, after the man- 

 ner of birds. It was indeed necessary, on account of the 

 length of the fore limbs, to place the Sauropoda on all 

 four feet ; but analogy caused it to be supposed that the 

 limbs were disposed, with reference to the vertical plane 

 of the body, similarly to those of the bipedal dinosaurs. 

 The conception of a creeping dinosaur was hardly to be 

 entertained. The straight femora of these reptiles, having 

 the head and the great trochanter moderately developed, 

 lent probability to the idea. 



If the straightness of the femora is relied on to support 

 the correctness of the prevailing restorations of the 

 Sauropoda we may call attention to the equally straight 

 femora of sphenodon and of the lizards. Notwithstand- 

 ing the great size of the carnivorous dinosaur Allosaurus 

 and the fact that the whole weight of its body was com- 

 monly borne by the hinder limbs alone, its femora are con- 

 siderably bent. The prominence and the height of the 

 great trochanter of the Sauropoda do not appear to be 

 such as to have prevented the femora from standing out at 

 right angles with the body. Both the head of the femur 

 and the acetabulum were doubtless invested with much 

 cartilage, so that we can not now be wholly certain about 

 their form and fitting. The same may be said regarding 

 certain other articulations of the limbs. Hatcher 11 has 

 spoken of the character of the articulations and he has 

 expressed the opinion that the habitual support of the 

 body in the air could not have .failed to produce closely 

 applied and well-finished articulations, and Osborn had 

 previously expressed the same idea. 12 There is indeed 

 a great difference between the articulations of the limbs 

 of the Sauropoda and those of the Theropoda, such as 

 Allosaurus and Ceratosaurus. 



