70 A BOOK OF-WHALES 



symphisis of the mandibles. Another line culminates 

 in the Narwhal, Mono don, where all the teeth have 

 vanished in the adult animal save the well-known 

 tusk, and an accompanying tusk of smaller size, some- 

 times equally developed, in the upper jaw ; in this 



FIG. 16. SERIES OF LOWER JAWS TO ILLUSTRATE 

 GRADUAL DIMINUTION OF TEETH. 



(From van Beneden and Gervais.) 



a. Beluga. b. Grampus. c. Berardius. 



d. Mcsoplodon. e. Monodon. 



