90 STRUCTURE OF THE VERTEBRATES 



are the largest land animals, the legs being modified into straight 

 columns with little flexion at the joints, a specialization in corre- 

 lation with the great weight of the body. The Indian elephant 

 is more easily tamed, although progress has been made in train- 

 ing the African species for work. Most circus elephants are of the 

 Indian variety. Judging by their brain capacity the elephant is 

 a rather low order of mammal, and experiments indicate that 

 stories of their intelligence are highly colored. Several extinct 

 families of proboscideans are known, including the Mastodon 

 and INIammoth, the latter a true elephant more highly specialized 

 than the recent forms. 



Order Sirenia. The manatees and dugongs are herbivorous 

 aquatic mammals. Most of them inhabit the sea, although they 



Manatee (Sirenia) 

 Fig. 38. Order Sirenia, aquatic, herbivorous placentals. 



may go farther up rivers than the brackish waters; and some 

 are apparently limited to fresh water. The manatees are found 

 in the Atlantic Ocean and its tributaries on the shores of Africa 

 and the warmer parts of America. The sirenia gave rise to the 

 mermaid myth, for when a dark head rises above the water, 

 and the mother is seen holding her young in her flippers, the 

 illusion is sufficient to mislead the average seaman. And the illu- 

 sion is complete when the animal dives and the flukes of the 

 tail are seen. 



Order Cetacea. The cetacea are the whales and their allies. 

 They are the largest living animals, and from the standpoint 

 of mass are probably the largest which have ever existed. The 

 herbivorous dinosaurs were longer but not so large. Some whales 

 reach a length of ninety feet or more, while the smaller por- 

 poises are only a few feet long. The young are born with the 



