HISTORY OF THE ARTIODACTYLA 419 



In Recent North America there are four or five species of 

 sheep (Ovis) which are confined to the mountainous and broken 

 areas of the western part of the continent and extend from 

 Alaska to Mexico. The "Bighorn" or Rocky Mountain 

 Sheep {Ovis canadensis) is characterized by great, spirally coiled 

 horns in the rams, in the ewes the horns are very much smaller 

 and nearly straight ; the other species differ but shghtly from 

 this type. The species 0. canadensis has been foimd in the 

 Pleistocene, but nothing further is known of its history. 

 Evidently, the sheep were late inmiigrants. 



"The geographical distribution of wild sheep is interesting. 

 The immense mountain ranges of Central Asia, the Pamir and 

 Thian Shan of Turkestan, may be looked on as the centre of 

 their habitat." "Sheep are essentially inhabitants of the 

 high mountainous parts of the world, for dweUing among 

 which their wonderful powers of climbing and leaping give 

 them special advantages. No species frequent by choice either 

 level deserts, open plains, dense forests or swamps. By far 

 the greater number of species are inhabitants of the continent 

 of Asia, one extending into North America [should read, foxir 

 or five] one into Southern Europe and one into North Africa. 

 . . . No remains that can be with certainty referred to the 

 genus [Ovis] have been met with in the hitherto explored true 

 Tertiary beds, which have yielded such abundant modifications 

 of Antelopes and Deer." ^ 



The only other division of the family which is represented 

 in North America is that of the bisons, of which the fast vanish- 

 ing remnant of a single species ^ {Bison bison) is aU that is left 

 of what was once an extensive and varied assemblage. The 

 bisons differ from the true oxen in the form and structure oi 

 the skull, in the shoulder-hump, which is produced by the very 

 long spines of the dorsal vertebrae and in consequence of which 

 the back slopes downward from the shoulders to the croup. 



' Flower and Lydekker, op. cit., pp. 355 and 357. 



' The Woodland Bison of Canada is now regarded as a distinct species. 



