EVOLUTION OP WHALES 



317 



((Fig. 101, 6), while the jaws have become greatly elongated. The 

 teeth have in some cases completely disappeared, as in the whale- 



FIG. 162. Skull of the Dolphin, X . (From British Museum Guide.) 



bone whales (except for total vestiges), while in others they are \ 

 present in large numbers but have lost the typical mammalian 



FlG. 163. Dorsal and lateral views of the Skull of a primitive Whale, 

 Prozeuglodon atrox, X ^T. (From British Museum Guide.) 



differentiation into incisors, canines, premolars and molars, being 

 represented by a continuous and uniform series, all of which are 

 conical in shape and single-rooted. Such teeth occur in both 



