SCIENCE FROM AN EASY CHAIK 



In the upper Tertiary we find the remains of a 

 kind of horse (the Hipparion), with well-developed 

 " petti-toes " (like those of a pig) on each side of the 

 big central toe (Fig. 10). In the middle Tertiary we 

 find smaller ancestral horses, 

 with three toes of nearly equal 

 size, and in the lower Tertiary 

 a horse-ancestor as small as 

 a fox-hound (the Hyraco- 

 therium), with four toes on its 

 front foot and three on its 

 hind foot. Coming very close 

 to this in general character 

 is another small extinct animal 

 of the same age, with five 

 toes on each foot. As the 

 toes have dwindled in number 

 and size, leaving at last only 

 the big central toe (as we 

 pass upward from the small 

 ancestors to the big modern 

 horse), so the cheek-teeth, too, 

 have changed. At first they 

 HIP PAR. ON HORSE had shallow crowns and divided 



FIG. 10. -To the left, the fore-foot fangs, and Showed four pro- 

 of the horse-ancestor, Hipparion, minences on the crown which 

 showing three toes: to the right were ^ if at all worn down 

 the back view of a long bone of 



a modern horse's foot, with rudi- during life. But as the horse 

 ments of outer toes, called splint- became a bigger animal and 

 bones - took to eating coarse tooth- 



wearing grass, his teeth became deeper, and continued to 

 grow for a long time, whilst the crown was rubbed down 

 by the hard food, and a curiously complex pattern was 

 brought into view by the exposure of the irregular bosses 

 of the crown in cross section. And, meanwhile, the size 



