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 Hyomoschus 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 primative 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 omniv- 
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, 
