the Skeleton of Diplodocus Carnegiei. 359 



It may be worth while briefly to indicate the views put forward 

 by Dr. J. B. Hatcher, 0. C. Marsh, and Professor H. F. Osborn. As 

 Hatcher points out in his valuable paper above referred to, Marsh 

 was the first to advance the aquatic habits of Diplodocus, having 

 considered the position of the narial openings (nostrils) quite on the 

 top of the skull, as suggestive of such habits. But this conclusion, 

 some authorities think, is more or less shaken by the fact that certain 

 mammals show rather similar conditions without being aquatic. 

 Again, in dealing with the skeleton of Cetiosaurus, he lays stress 

 on the open cancellous tissue of the vertebrae and limbs. At the 

 time it was thought that they showed no trace of any medullary 

 cavity. But more recent researches have shown that some 

 of the Sauropoda had a medullary cavity. Dr. Hatcher thought 

 that, if modified at all for aquatic habits, it was in the direction 

 of more open and cancellous tissue, even than that which obtains 

 in the Cetacea, and calculated not only to give greater buoyancy 

 to these massive quadrupeds when in the water, but in addition to 

 give the greatest possible surface for muscular attachment com- 

 patible with the required rigidity and with the least possible weight. 



In the same paper Hatcher sums up his conclusions with regard to 

 the locomotive powers of Diplodocus in the following words: " That 

 the movements of the animal when on land were decidedly slow and 

 clumsy ; for, had Diplodocus and its ancestors been addicted to 

 terrestrial life, the habitual support of so massive a body in so light 

 a medium as the atmosphere would scarcely have failed to produce 

 closely applied and well-finished articular surfaces to the limb- 

 bones similar to those which obtain in such members of the 

 Theropoda as are of undoubted terrestrial habits." 



In his second paper (Mem. Carnegie Inst., vol. ii, p. 58) Hatcher 

 revises his previous conclusions. He disagrees with Osborn's 

 conclusion about a tail-fin. The limbs, he thought, were essentially 

 terrestrial. They are not abbreviated or subordinated, as in the 

 Amphibia and Beptilia and some aquatic Mammals. So he thinks 

 the limbs were first of all ambulatory to give support to the body. 

 He also believes his conclusions to be strengthened by a study of 

 the fossil remains found with Diplodocus and the nature of the rocks 

 in which they occur, viz. sandstones. Thus we see how the various 

 authorities differ among themselves. One more argument may be 

 mentioned here. He refers to the deeply pitted articular surfaces of 

 the various parts of the appendicular skeleton (i.e. the four limbs 

 and the pectoral and pelvic girdles). These, he thinks, may mean 

 that there were thick cartilaginous pads interposed between such 

 surfaces at the various joints of the limbs and feet. This want of 

 closely-fitting and well-defined articular surfaces would appear to 

 afford additional evidence of aquatic habits. Here the writer would 

 like to point out that an animal may be very largely aquatic in habit 

 without showing much trace of such habit in its skeleton. For 

 instance, the hippopotamus, the water-rat, water-hog, otter, polar 

 bear, and crocodile are largely aquatic, and yet if known only by 

 fossil remains, would be put down as entirely terrestrial ! One has 

 to be cautious' in drawing- conclusions. American naturalists have 



