188 



DINOCERATA. 



the outer dig-its left the ground, ceased to be of use, and were lost, 

 except as splint hones. The foot of the existing horse (figures 1G6 and 

 1G7) shows the best example of this reduction in the Perissodactyls, as 

 it is the most specialized known in the Ungulates. 



H M M IV M N 



Figure 1G6. — Left fore foot of horse (S^wm cafcaWus, Linnrtiis). 

 FiGlTRH 107. — Left liind foot of same. 



Both figures are one-eighth natural size. 

 FiiiURE 1G8.— Left fore foot of goat (Copra /nVcjts, Linnaius). 

 Figure 169. — Left hind foot of .same. 



Both figures are oue-lifth natural size. 



(G.) In the Artiodactyl foot, the reduction resulted in the gradual 

 diminution of the two outer of the four remaining toes, the third and 

 fourth doing all the work, and thus increasing in size and power. The 

 fifth digit, for the same reasons as in the Perissodactyl foot, first left the 

 oTOund, and became smaller. Next, the second soon followed, and these 

 two gradually ceased to be functional, or were lost entirely, as in some 

 of the Artiodactyls of to-day. The feet of the goat, figures 1G8 and 1G9, 

 above, show this extreme reduction. 



As the author has shown elsewhere, these reductions of the feet, and 

 of the entire limbs, led to greater strength and speed, as the motion, 

 before irregular, gradually came to act in a single plane. 



