54 THE AMERICAN BISONS. 
bison of the Plains, the crowns of the teeth present a nearly even surface, 
every part of the tooth being worn to nearly the same level. In the re- 
mains from Big-bone Lick, however, the crown surface wears into a series of 
deep transverse serrations, the ridges of which often rise a fourth of an inch 
above the intervening hollows. The difference between the two in this 
respect is strikingly great (see Plate [X*), and evidently relates to the dif- 
ferent character of the food obtainable in the two districts. The bison of 
the Plains necessarily feeds wholly upon short, fine grasses, which rarely 
attain a height of more than a few inches, and are consequently at times 
more or less sprinkled with sand and dust. The Ohio Valley, on the con- 
trary, is a region of rank herbage, and tall succulent grasses. The Plains 
bison must take with its food more or less gritty material,t which tends not 
only to wear the teeth down evenly, but far more rapidly than was the case 
in the Ohio Valley, the teeth in the Plains bisons generally being very much 
worn even in middle-aged animals, while in very old animals the teeth are 
often worn down to the fangs. Even the temporary set become wholly worn 
out before they give place to the permanent series. Nothing of this kind has 
been observed in specimens from Big-bone Lick, even in the oldest individuals. 
Geographical Distribution. — Since the geographical distribution of the Amer- 
ican bison, past and present, is treated at length in a subsequent chapter de- 
voted especially to the subject, a few words only on this point will suffice in 
the present connection. The habitat of the bison (see Map I) formerly ex- 
tended from Great Slave Lake on the north, in latitude about 62°, to the north- 
eastern provinces of Mexico, as far south as latitude 25°. Its range in Brit- 
ish North America extended from the Rocky Mountains on the west to the 
wooded highlands about six -hundred miles west of Hudson’s Bay, or about 
to a line running southeastward from the Great Slave Lake to the Lake of the 
Woods. Its range in the United States formerly embraced a considerable area 
west of the Rocky Mountains, its recent remains having been found in Oregon 
as far west as the Blue Mountains, and further south if occupied the Great 
Salt Lake Basin, extending westward even to the Sierra Nevada Mountains, 
while less than fifty years since it existed over the head-waters of the Green 
and Grand Rivers, and other sources of the Colorado. East of the Rocky 
Mountains its range extended southward far beyond the Rio Grande, and 
* This Plate also contains figures of the milk-dentition. 
+ In the teeth of specimens from the Plains I have found sharp angular particles of quartz sand wedged 
into the cavities of the teeth. 
