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 IX*), 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,! 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 [) formerly ex- 

 tended from Great Slave Lake on the north, in latitude about (VI . to the north- 

 eastern provinces of Mexico, as far south as latitude 2o°. Its range in Brit- 

 ish North America extended from the Rocky Mountains on the wesl to the 

 WOoded highlands about six hundred miles wesl of Hudson's Bay. or about 

 to a line running southeastward from the (ireat 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 die Blue Mountains, and further south it occupied the Great 

 Salt Lake Basin, extending westward even to the Siena Nevada Mountains, 

 while less than fifty years since it existed over the head-waters of the Greeu 

 and Grand Rivera, and other source- of the Colorado. Easl of the Rocky 

 Mountains its range extended southward far beyond the Rio Grande, and 



• Tlii- Plate also contains figures "t" tin- milk dentition 



t In the teeth of ip <i" Plaint I have found sharp angular particles ol quarti sand 



into the i a% itie« ■ •! the t. eth 



