MAMMALS OF MINNESOTA. 255 



In the peccaries of South America the reduction is carried 

 still farther. The inner toe of the hind foot disappears and 

 the metatarsals are partially united. In the genus Hyomos- 

 chus (Chevrotain) a similar reduction is exhibited. Tibia and 

 fibula are present and distinct, the metacarpals are distinct, 

 while the corresponding bones in the posterior extremity are 

 united more or less throughout. All other living ruminants 

 (and the Hyomosckus is a very old type, its bones being found 

 in the Eocene period) have the metatarsals and metacarpals 

 fully united, only a groove indicating the line where the two 

 bones have united during the embryonic life of the animal. 

 Giraffes exhibit the last stage in the process. Here the bones 

 are fully united and the accessory hoofs disappear. The history 

 thus preserved in a fragmentary way in the living examples of 

 the Artiodactyla is completed and supplemented in the records 

 of paleontology. 



We discover a marked similarity with the history of the de- 

 velopment of the horse in the above account of the modifica- 

 tion of the hoof in the even- toed group. 



The primatwe artiodactyle, it may be presumed, had 44 

 teeth, three incisors, one canine, and seven teeth in the molar 

 series in each half of the jaws. Even in ruminants which 

 suffer the greatest reduction from the type, the rudiments of 

 these teeth are found in the embryo and simply fail to develop. 



In the Eocene period there existed a curious form called 

 Anoplotherium which had a full set of teeth in an unbroken 

 series. A reduction in the number of teeth during the ages is 

 not less remarkable than that of the digits as above described, 

 and here too modern representatives of the various stages of the 

 process remain. In the swine there are six incisors above and 

 below, the hippopotamus has but four above, the camel only 

 two, and cattle none. The reduction in the number of the 

 teeth and especially in the canines is indicative of a change 

 from omnivorous to herbivorous habits. It would seem, more- 

 over, that when the incisors cease to be developed into weapons 

 either offensive or defensive, there is a tendency to produce 

 excresences from the skull above in other words horns, ant- 

 lers, or their equivalents. 



The number and structure of the teeth varies with the com- 

 plexity of the digestive organs. In the swine and other o mniv- 

 orous ungulates the stomach is simple while in the ruminants 

 it is divided more or less fully into four sacks or compartments 

 which have various functions. The most important parts are, 



