THE SKELETON IN MAMMALIA. THE TEETH. 427 



Europe and Patagonia is allied to the Sperm whale, but has 

 teeth in both jaws. In the Grampus Orca, the teeth number 

 about ^|, and are very large and strong. In some forms the 

 teeth are very much reduced in number ; thus in Mesoplodon 

 the dentition consists simply of a pair of conical teeth borne 

 in the mandible. In the Narwhal Monodon the dentition is 

 practically reduced to a single pair of teeth, which lie horizon- 

 tally in the maxilla, and in the female normally remain perma- 

 nently in the alveoli. In the male the right tooth remains 

 rudimentary, while the left is developed into an enormous 

 cylindrical tusk marked by a spiral groove. Occasionally both 

 teeth develop into tusks, and there is reason for thinking that 

 two-tusked individuals are generally or always female. In the 

 extinct Squalodon the dentition is decidedly heterodorit, and 

 the molars have two roots. The dental formula is 



i =- c pm m -= , total 60. 



It is probable that the homodont condition of modern Odonto- 

 ceti is not primitive, but due to retrogressive evolution. 



UNGULATA. 



Just as in the Cetacea a piscivorous dentition is most 

 typically developed, so the Ungulata are, as a group, the most 

 characteristic representatives of a herbivorous dentition in its 

 various forms. 



UNGULATA VERA. 



ARTIODACTYLA. As regards the living forms, the Artio- 

 dactyla can be readily divided into two groups, namely those 

 with bunodont and those with selenodont teeth. It has, how- 

 ever, been shown that selenodont teeth always pass through 

 an embryonic bunodont stage 1 . The bunodont type is best seen 



in Pigs and Hippopotami and such extinct forms as Hyotherium. 



/2 3\ } 43 



In Hippopotamus the dental formula is i , - -=* c - pm 7^0- 



(1 o) 1 4 o 



1 J. Taeker, " Fur Kenntniss der Odontogenese bei Ungulaten."- Dorpat, 

 1892. 



