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THE AMERICAN NATURALIST [Vol. XLV 



principal difference is found in the fact that the upper 

 end of the ulna extended across the lower end of the 

 humerus and has a concavity in front for the head of the 

 radius. The ulna and radius appear to have been more 

 closely hound together at the lower ends than in the croc- 

 odile; nevertheless, the hones of the two reptiles re- 

 semble one another closely. When to those of the sauro- 

 pod a humerus of corresponding size is fitted, with the 

 outer (anterior) condyle in contact with the head of the 

 radius, the leg is strikingly like that of the crocodile. 

 In my opinion, Marsh's arrangement of the bones of the 

 fore leg of Brontosauru.s* is more nearly correct than 

 later restorations of this limb in the same animal and in 

 Diplodocus. In the figures referred to, the humerus, in 

 the middle of the step, presents the dorsal surface out- 

 ward; whereas, in the Pittsburgh and New York res- 

 torations this surface looks backwards and the deltoid 

 border looks outward. If Marsh's figure were modified 

 so that the humerus were horizontal or nearly so, the 

 leg would have nearly its natural position. 



Various opinions are held regarding the question 

 whether the sauropods were strictly aquatic, strictly ter- 

 restrial or amphibious. In my paper published in the 

 Proceedings of the Washington Academy of Science I 

 called attention to a figure that illustrates Cope's views 

 and to another published by Matthew that elucidated 

 Osborn's ideas. Dr. Matthew's views seem to differ 

 from those of Osborn in that the former maintains that 

 these reptiles usually preferred not to be wholly sub- 

 merged and that they could not leave the water without 

 endangering the integrity of their limbs. He finds his 

 reasons for his opinion as to the depth of the water pre- 

 ferred in the fact that the bones above a line drawn from 

 the hip joint to the shoulder blade are of light construc- 

 tion, while those below this line are thick and heavy. 

 This line is his "water-line" and indicates the average 

 depth of the water haunted by these reptiles. The heavy 



s The Dinosaurs of North America, PI. XLII. 



