30 EVOLUTION OF THE HORSE 
PARALLEL EVOLUTION IN OTHER RACES. 
It is interesting to observe that while the evolution of the 
Horse was progressing during the Tertiary period in North 
America another group of hoofed animals, the Litopterna, now 
extinct, in South America evolved a race adapted to the broad 
plains of Argentina and Patagonia and singularly like the Horse 
in many ways (see exhibit in A-case in centre of hall). These 
animals likewise lost the lateral toes one after another, and con- 
centrated the step on the central toe; they also changed the form 
of the joint-surfaces from ball-and-socket to pulley-wheel joints; 
they also lengthened the limbs and the neck; and they also 
lengthened the teeth, and complicated their pattern. Unlike the 
true Horse, they did not form cement on the tooth, so that it was 
by no means so efficient a grinder. This group of animals native 
to South America became totally extinct, and were succeeded by 
the horses, immigrants from North America, which in their turn 
became extinct before the appearance of civilized man. 
Many of the contemporaries of the Horse in the northern 
hemisphere were likewise lengthening the limbs, lightening and 
strengthening the feet, elongating the tooth-crowns to adapt 
themselves to the changing conditions around them, but none 
paralleled the Horse Evolution quite so closely as did the pseudo- 
horses of South America. But the camels in America, the deer, 
antelope, sheep and cattle in the Old World progressed on much 
the same lines of evolution, although their adaptation was not to 
just the same conditions of life. 
