82 MOUNTAIN FAUNAS 
described the way in which the animals push their way 
through snow, or across glaciers, or through icy glacial 
torrents. They present a remarkable instance of 
adaptation to very unfavourable conditions, but in this 
connexion it is important to remember the great extent 
of the plateau of Tibet, and its great uniformity. 
The yak is the only member of the cattle group with 
special adaptations to mountain life. Passing to the 
sheep we find that there are eleven well-defined wild 
species. Of these, eight inhabit various mountain chains 
and plateaux in Asia, one, the Indian urial, extending 
to relatively low ground in the Punjab and Sind ; one 
form is found in the Rocky Mountains, but this, the 
Bighorn, is so closely related to the wild sheep of 
Kamchatka as to suggest a former land connexion 
across the Bering Strait. Of the remaining two species, 
one, the mouflon, occurs in mountain regions in Sardinia 
and Corsica, and the other, the Barbary sheep, is found 
on the southern slopes of the Atlas Mountains in Africa. 
We are thus justified not only in saying that sheep are 
definitely mountain animals, but also that the home of 
the genus is the mountainous regions of Central Asia, 
only the urial extending south of the Himalayas. The 
habits of all are generally similar, and have been 
already alluded to. To the preceding description we 
may add a brief note on the wild sheep called argali, of 
which one form (Ovis ammon) is found at moderate 
elevations in Mongolia, while the other (Ovis hodgsoni) 
occurs at great heights on the Tibetan plateau. Both 
are large animals, reaching the size of a small donkey, 
and having short and close hair. The food consists of 
grass, mingled in winter with mosses and lichens, and, 
like the reindeer of the tundra, the animals in winter 
seek exposed positions where the wind sweeps away 
