8 4 



WATER REPTILES OF THE PAST AND PRESENT 



aquatic reptiles and mammals. The paddles resemble those of the 

 ichthyosaurs more nearly than those of any other reptile, and it 

 was doubtless this superficial resemblance which so long deceived 

 the early anatomists as to the affinities of the two orders. Unlike 

 all other aquatic animals, however, the plesiosaurs have the hind 

 limbs nearly or quite as large as the front ones, and they doubtless 

 were equally effective in function. The humerus and femur are 

 always elongate, though broad and massive. In no other aquatic 

 animals, save the marine turtles, do we find these bones relatively 



Fig. 37. — Pelvic girdle of Elasmosaurus: p, pubis; is, ischium; il, ilium 



so long and strong; they are very short in the cetaceans, the sire- 

 nians, the ichthyosaurs, mosasaurs, thalattosaurs, and the marine 

 crocodiles, in front at least. The strong muscular rugosities of 

 the plesiosaurian bones are very suggestive of powerful swimming 

 muscles. 



The bones of the forearms and legs, the wrists and ankles are 

 all polygonal platelets of bones, closely articulating with each other. 

 The finger and toe bones have a more elongated, hour-glass shape 

 than those of the ichthyosaurs, resembling more nearly those of the 



