THE ORDERS OF MAMMALS 439 



western North America. Their horns are hollow, branched, 

 and shed annually. 



The ox family contains the gnus, Rocky Mountain goats, 

 sheep, goats, musk oxen, and bison. These are all ruminants, 

 and both males and females usually possess unbranched, hollow 

 horns, which fit over bony prominences on the skull and are not 

 shed annually. The best-known American forms are the bison, 

 musk ox, bighorn, and mountain goat. 



FIG. 307. Bison. (Photo, by Hegner.) 



The bison (Fig. 307), up to the year 1870, ranged over a lar'ge 

 part of the Great Plains and other portions of North America. 

 It was persistently hunted, chiefly for its hide, until most of its kind 

 had been killed. In 1903 it was estimated that about six hun- 

 dred wild individuals and one thousand captive specimens still 

 existed. The musk ox lives on the Arctic barrens of North Amer- 

 ica. It has a long, shaggy coat, and the male has a strong, 

 musky smell. The Eskimos use it for many purposes. The 

 bighorn, or mountain sheep (Fig. 308), is an inhabitant of the 

 slopes of the Rocky and Sierra mountains above timber line. It 

 seeks the more sheltered valleys in the winter. The mountain 



