550 



THE AM ERIC AX XATURALIST 



[Vol. XLIV 



todon, gigantic mammals of widely diverse stocks, in 

 Stegosaurus and Triceratops among the dinosaurs, and 

 an approach towards it in various other groups. The 

 modern horses, rhinoceroses, cattle and other large ani- 

 mals, and most of the very large extinct mammals show 

 a distinct approach toward these proportions as com- 

 pared with their smaller and more agile ancestors ; so too 

 do the gigantic Truehutlon and Tyraunoxaurus as com- 

 pared with their smaller and more agile ancestors or rel- 

 atives, Laosaimis, Campiosnurns, and Allosaurus. 



On the other hand, a glance at a lizard femur shows 

 that the straight shaft is associated here with a wholly 

 different position of the proximal and distal articulations 

 and of the trochanters by which the limb is moved. The 

 distal articulations for the tibia and fibula are on the 

 back of the femur, not on its end; the great trochanter 

 for the hip muscles projects outwards from the shaft 

 instead of upwards in line with it ; the feet are long and 

 the toes relatively elongate; there is very little padding. 



The shaft of the femur is nearly straight in the aquatic 

 turtles and the articulation for the lower limb is quite 

 distal in position; but the trochanter projects upward, 

 the limb is carried outward from the body and more or 

 less straight. In the land turtles and in the crocodiles 

 the femur has a strongly curved shaft, bent downward at 

 the distal end, the limb still projecting outward from the 

 body but flexed sharply downward at the knee. Here 

 then are two distinct methods by which a swimming limb 

 may be converted into a crawling limb. 



The straight-shafted femur does not per se prove that 

 Diplo floats walked in any of the various ways that mam- 

 mals walk. But taken in connection with the numerous 

 other adaptive resemblances in form and proportions of 

 the bones of the hind limb, feet and pelvis, to the ele- 

 phants and other gigantic mammals and reptiles cited, 



Diplodocus walked like an elephant as to its hind limbs. 



Dr. Hay's next point appears to be a strong one. He 

 observes that if we compare the femora of such dinosaurs 



