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 G^idde to the Horse 

 Family, by Mr. E. 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, 1 

 " 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 

 1 The Horse: A Study in Natural History. (London, 1891.) 



