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THE AMERICAN NATURALIST [Vol. XLIV 



while mammals walk; that Diplodocus is a reptile and 

 resembles the lizards and crocodiles far more closely than 

 it does any mammals in the details of construction of the 

 shoulder- and hip-girdles, limbs and feet. Therefore, it 

 should be posed like one of the larger lizards, except for 

 the long neck, which he compares to the long-necked birds 

 and poses in accordance. A sketch restoration and a 

 number of diagrammatic drawings illustrate his views. 

 The subject appears, frankly, to be somewhat outside the 

 range of his studies, and his comparisons are not broad 

 or thorough enough to be at all convincing. 



His criticisms are very effectively and completely 

 answered by Dr. Abel and Dr. Holland. These authors 

 point out that while the dinosaurs were reptiles and as 

 such their bones were constructed upon the reptilian plan, 

 yet they form a group apart, differing from other reptiles 

 and in many respects resembling the struthious birds; 

 that these resemblances, especially as regards the con- 

 struction of pelvis and hind limbs, leave no reasonable 

 doubt that the typical dinosaurs walked pretty much as 

 do the great ground birds ; that the limbs of Diplodocus 

 and its allies differ from the normal dinosaur type in a 

 marked superficial and adaptive resemblance to the ele- 

 phant, indicating a quadrupedal " rectigrade " mode of 

 motion; that the skeleton articulates satisfactorily in this 

 pose and that the attempt to articulate it in the pose of a 

 crocodile or lizard involves either a demonstrably false 

 interpretation of parts, or a disarticulation of the joints 

 which proves such a position to be highly abnormal if 

 not utterly impossible for the creature to assume. 



Dr. Hay's contributions to the discussion— the article 

 cited and an earlier one in the American Naturalist— 

 are worthy of more careful consideration. Hay is a high 

 authority on fossil vertebrata, especially upon Chelonia 

 and fishes, and has recently devoted considerable study to 

 the dinosaurs. He recognizes the fact that the dinosaurs, 

 while pertaining to the class Reptilia, form a group apart, 

 with many analogies to the birds ; that many dinosaurs 

 did walk with the body clear of the ground, and that many 



