MAMMALIA. 317 



of other mammals. The posterior extremities are absent, 

 and the body terminates in a broad horizontal fin. (Fig. 217.) 

 The bodies of the cervical vertebra are much flattened, and 

 the portion of the temporal bone, which contains the internal 

 ear, is united to the temporal by ligaments. 



This order contains three families. 



The BAL^NTDJE (or Whales) have an enormous head; 

 the jaws are provided with horny lamina, instead of teeth. 

 Three species of Balcenoptera are found in the sub-apennine 

 stage of Italy, and one of Balcena from the same stage of 

 Piedmont and the United States. Two species are found in 

 the pleistocene of Herne Bay, and the diluvium of England. 



The DELPH1NIDJ3 (or Dolphins) have the head small, 

 and the jaws provided with numerous sharp conical teeth 

 (fig. 218.) "We know two extinct genera of this family, 

 Ziphius, from the eocene of Provence, and Balamodon, from 

 the same stage in England. From the upper tertiary beds 

 of France, England, and America, species of Delphimis, 

 Monodon, and PJimeter have been obtained. 



FIG. 218. Delphinus delphis. 



The MANATIDJB (or herbivorous whales) have molar teeth 

 with flat crowns. They frequent the mouths of the great 

 rivers in the tropical regions of the Old and New Worlds. 

 The Dugong (JHalicord) and the Lamantin (Manatus) are its 

 living types. We find fossil species of these genera in the 

 newer tertiaries of Switzerland and of ISTorth America. This 

 family contains several extinct genera, as Metaxytherium, of 

 which an entire skeleton was found at Beaucaire, and dif- 

 ferent portions in the falunian stage of Touraine. 



