The Evolution of the Horse. 
127 
and, indeed, is one of the most remarkable instances of speciali- 
sation or deviation from the usual type, in accordance with 
special conditions of life, which is known. It can be demon- 
strated, both by the structure of the foot itself, and also by an 
examination of the various intermediate fossil species, that this 
toe corresponds to the middle or third of the complete, typical 
five-toed foot — the " ring fiuger " of man ; and there is very 
strong evidence to show that, by a gradual concentration of all 
the power upon this toe, and the concurrent dwindling away, 
and final disappearance, of all the others, the present condition 
of the horse's foot has been produced. 
The- small, horse-like animals of the Eocene period, with 
five, four, or three toes on each foot, have already been men- 
tioned. In the next age of the world's history — the early Mio- 
cene period — the animal most like the existing horse was the 
Anchitherium, the remains of which are found in a fossil state 
both in Europe and America. In this genus there were three 
well-developed toes reaching the ground on each foot, and the 
bones of the fore-arm (radius and ulna), and those of the leg 
(tibia and fibula), were fully developed and distinct. This animal 
was succeeded by animals which have been named Hipparion, 
Ilippotherium, Protohippas, and Plioliippus, of which there were 
many kinds, differing slightly in form and proportions, and in 
the characters of the enamel foldings of their molar teeth, but 
resembling each other in the structure of the feet. In these 
the lateral toes, though containing the full number of bones, 
were much reduced in size, and did not reach the ground, but 
were suspended to the outside of, and rather behind, the large 
middle one, like the rudimentary outer toes of the deer, or the 
short, first digit (" dew-claw ") of the dog. Horses, or, rather 
horse-like creatures, with this structure of feet, were no longer 
met with when the Pleistocene, or latest geological period, set 
in ; but then, for the first time, appeared the true horse, in its 
development exactly, or very nearly, as we know it now. The 
outer toes (second and fourth) were reduced to rudiments of the 
metacarpals or metatarsals only — the so-called " splint bones " — 
entirely concealed beneath the skin, while the middle or third 
toe was greatly elongated, and had its last bone (ungual 
phalanx, os pedis, or " coffin-bone ") much expanded in breadth. 
At the same time, the stability of the fore-arm and leg was 
increased by the two bones contained in each in the primitive 
forms being completely fused into one. Even since the Pleis- 
tocene period a change has taken place, as in horses of the 
present time the lateral rudimentary metacarpals, or splint 
bones, though independent bones in the young animal, have a 
