316 OUTLINES OF EVOLUTIONARY BIOLOGY 



fish-like ancestors. 1 The fore limbs have become converted into 

 paddles while the hind limbs have entirely disappeared externally 



FIG. 160. Skull of Dinotherium giganteum, Lower Pliocene, X T V (From 

 Smith Woodward's " Vertebrate Palaeontology," after Kaup.) 



(Fig. 161). The tail has become flattened out into a horizontal 

 \\fin and there is frequently a well developed dorsal fin. The skull 



FIG. 161. The Dolphin, Delphinita delplm, 



Guide.) 



(From British Museum 



has undergone very curious changes. The brain case is rounded 

 and strongly arched (Fig. 162) and the nasal apertures or blow- 

 holes lie far back, at or near the highest point of the he 



I Compare Chapter XVII. 



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