244 ' EXTINCT MONSTERS 
the Mesohippus (see Fig. 90). One finger has been dropped, 
and the skull is decidedly bigger. Here we see the middle 
or third digit getting larger. Unfortunately the skull of 
Protohippus, which is the next stage, is unknown; but we 
have the feet, of which a fore foot is shown in Fig. 89. Here 
the centre digit is much bigger, and this increase becomes 
still more striking in the Hipparion: until at last, in the 
modern horse, this one digit is supreme, and the others are 
only represented by the two feeble “splint bones” that were 
for so long a puzzle to anatomists. Now we see in them the 
vestiges of former digits no longer used for walking on. The 
outline restorations 1, 2, 3, 4, 5, 6, in Fig. 90, may be studied 
in connection with the bones in Fig. 89, Hipparion was of the 
size of a donkey. 
South America had some peculiar horses of its own; for further 
information the reader should consult the Gwide to the Horse 
Family, by Mr. R. Lydekker, F.R.S., to be obtained at the Natural 
History Museum (price one shilling). 
Speaking of these changes, the late Sir William Flower said,} 
“Short, stout legs and broad feet, with numerous toes, spreading 
apart from each other when the weight of the creature is borne on 
them, are sufficiently well adapted for plodding deliberately over 
marshy and yielding surfaces, and the tapir and the rhinoceros, 
which in the structure of their limbs have altered but little from 
the primitive Eocene forms, still haunt the borders of streams and 
lakes and the shady depths of forests, as was probably the habit of 
their ancient representatives ; while the horses are all inhabitants 
of the open plains, for life upon which their whole organisation 
is in the most eminent degree adapted. The length and mobility 
of the neck, position of the eye and ear, and great development of 
' The Horse: A Study in Natural History. (London, 1891.) 
