Chap. IV.] 



TEETH OF GET ACE A. 



special armature of the mouth by " whalebone ; 

 "but indications are presented both by palaeontology 

 and embryology which are sufficient to justify us in 

 believing that this 

 order was primi- 

 tively provided 

 with a heterodont 

 dentition. While 

 the dolphin has a 

 number of teeth 

 in both jaws ; the 

 sperm-w hale has 

 well - developed 

 teeth in the lower 

 jaw only; the 

 bottle-nosed whale 

 has never more 

 than four func- 

 tional teeth, and in 

 the narwal (Mono- 

 don) it is the male 

 only that has the 

 ordinarily single 

 tusk well de- 

 veloped ; this may 

 be as much as nine 

 feet long. Among 

 the whale-bone 

 whales teeth are 

 never more than 

 rudimentary, but 

 in the adult their 



place is taken by plates of " baleen," which are 

 set nearly at right angles to the axis of the mouth, 

 and have their free ends frayed out into a number 

 of stiff hairs, which make a most efficient strainer ; 

 the whale, in taking into its enormous mouth a 



Fig. 68. Teeth, of Horse ; A, Upper Jaw ; B, 

 Lower Jaw. 



