CETACEA. 505 



throughout life within the abdomen and there are no vesiculas 

 seminales. The teats are two in number and are placed upon 

 the groin. The head is generally of disproportionately large 

 size, and is never separated from the body by any distinct con- 

 striction or neck. The lumbar region of the spine is long, 

 and, as in the Sirenia, there is no sacrum, and the pelvis is 

 only present in a rudimentary form. There are no clavicles, 

 and some of the digits may possess more than three phalanges 

 each. Lastly, the adult is either destitute of teeth or is mono- 

 phyodont that is to say, possesses but a single set of teeth, 

 which are never replaced by others. When teeth are present, 

 they are usually conical and numerous, and they are always of 

 one kind only. 



The Cetacea may be divided into the three families of the 

 Balcenidcz or Whalebone Whales, the Delphinida or Dolphins 

 and Porpoises, and the Catodontida or Sperm Whales. Of these, 

 the BalcenidcE are often spoken of as the " toothless " Whales, 

 whilst the other two families are called the " toothed " Whales 

 ( Odontoceti}. 



Fig. 193. Skull of the Right Whale Bal&na mysticetus) after Owen. 



Fam. i. Balcenida. Tti*l?afo*jafa or Toothless Whales are 

 characterised by the total absence of teeth in the adult (fig. 

 193). Teeth, however, are present in the fcetal Whale, but 

 they never cut the gum. The place of teeth is supplied by a 

 number of plates of whalebone or " baleen " attached to the 

 palate ; hence the name of " whalebone Whales " often given 

 to this family. They are the largest of living animals, and 

 may be divided into the two sections of the Smooth Whales, 

 in which the skin is smooth and there is no dorsal fin (as in 

 the Greenland Whale), and the Furrowed Whales, in which 

 the skin is furrowed and a dorsal fin is present (as in the so- 

 called Finner Whales and Hump-backed Whales). 



