ADAPTATION OF EXTREMITIES FOR SWIMMING. 501 
far backwards, so as almost to occupy the position of the tail. 
In the Whale and its allies, on the other hand, the posterior 
extremities are almost entirely wanting, and the tail is greatly 
prolonged and expanded at its extremity (fig. 241). This 
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Fig. 241.—SxkeLtreton or Ducone. 
rcainion, however (which is in the horizontal direction, fig. 
242), is not supported by bones, except in its centre ; but it 
consists internally of cartilages and tendons, which last are 
longed from a set of very powerful muscles that are at- 
to the spine, and give to this organ an enormous force 
Fig. 242.—Ta1i-Fix or WHALE. 
d great variety of motion. The texture of the portion of it 
3y which the blow is usually given, is such that it can hardly 
injured ; it is so tough that it cannot be torn, and so free 
m. feeling, that a stroke of it against a hard substance gives 
pain to the animal. If it strike a boat across the middle 
ith its edge, the boat is cut asunder as clean and suddenly 
as if by one stroke of a giant axe ; whereas, if it strike with 
