610 ZOOLOGY. 
connects the deer family with the Bouidw, represented by 
the sheep, goat, antelope, gazelle, and ox. 
The domestic sheep (Ovis aries Linn.) is not a natural 
species, but an association of races whose. specific origin is 
obscure. Some authors regard the turf sheep of the stone 
age of Europe as the ancestor of the domestic sheep, as forms 
like it are now living in the Shetland Isles and in Wales. 
It was of small size, with slender limbs, and erect, short 
horns. This sheep was supplanted by a curved, large-horned 
form, the modern domestic sheep. This latter form is pos- 
sibly the descendant of the Ovis argali Pallas, of Asia, which. 
in North America is represented by the Ovis montana Cuvier, 
the Rocky Mountain sheep or big-horn (Fig. 530), still com- 
mon on the less accessible summits along the upper Missouri 
and Yellowstone Rivers, as well as the mountains of Wy- 
oming and Montana. 
In the same, though 
higher and more inac- 
cessible situations lives 
the rare mountain 
goat, Aploceros monta- 
nus Richardson, whose 
horns are jet black and 
polished, slender and 
conical, like those of 
the Swiss chamois. It 
is found sparingly in 
the higher summits of 
Fig. 529.—Horns at different ages of the Pron : 
horn Antelope, showing the hollow structure of the Rocky Mountains 
the horn when shed.—After Hays. and the Cascade range ; 
an individual has within a few years been shot on Mount 
Shasta, California. Passing by the gazelles and true an- 
telopes we come to another characteristic American an- 
imal, the musk sheep (Ovtbos moschatus Blainville, 
Fig. 531), now confined to the arctic regions. A closely 
allied species, Ovibos priscus of Riitimeyer, formerly during 
the post-glacial period existed in England, France, and Ger- 
many. Closely allied to the musk sheep is a fossil form 
(Boétherium of Leidy) which is regarded by Rtitimeyer and 
