248 THE MAMMALIA. 



final links in the chain of evidence that the Whale- 

 bone whales are the last members of a transformed 

 group which commenced with animals with four 

 toes and numerous teeth, and which by the gradual 

 diminution of the dentition have become Whale- 

 bone whales. 



. Still, the skull of the Whalebone whales shows so 

 much resemblance to that of the Dolphins and all 

 of the other toothed whales, that, were it not for 

 the discovery of teeth in the foetal animal, we should 

 be in doubt as to the unity of the two groups. 

 From the head of a dolphin only a few feet in 

 length, we may learn all about the peculiar trans- 

 formations just as well as from the head of a 

 Greenland whale. The mid jawbones (Fig. 45) 

 do not appear in front between the upper jaw- 

 bones, but are very much elongated, and fre- 

 quently lie somewhat irregularly, projecting beyond 

 the upper jawbone. The most striking changes, 

 however, are those of the middle head, and all this 

 can be traced to the rising up of the nasal cavities 

 in all other mammals these lie horizontally or 

 obliquely towards the front which form perpen- 

 dicular blow-holes close to the crown of the head. 

 Not only has the olfactory bone become raised, 

 but the nasal bones also, in most cases, have 

 been completely displaced from their position as 



