Life of Upper Lake Region. 135 



i 



a large increase in the depth of the body of 

 the tooth, so much so as to remind one at 

 once of the teeth of the living horse. 



That we may extend our comparison to 

 the feet of these Tertiary horses, let us study 

 the fossil shown on Plate XXIV. Here is 

 an Hipparion foot consisting of three meta- 

 carpal bones with corresponding phalanges, 

 the central one much the longest and by far 

 the most symmetrical; all three are articu- 

 lated both above and below, above to the 

 carpus or wrist, below to the phalanges or 

 toe bones. It has been stated in the last chap- 

 ter that the Anchitherium had three useful 

 hoofs for each foot, but this Hipparion fossil 

 shows the two outer metacarpals so short- 

 ened that his hoofs were plainly carried but 

 of reach of the ground as he traveled, giving 

 evidence that the horse of the Pliocene was 

 losing his second and fourth toes. 



If now we compare the same fossil with 

 the corresponding bones of the living horse 

 on Plate XXI, we will find a very marked 

 relative increase of the central metacarpal 



