The central digit of horses became increasingly stronger while the "side toes" became less important and are virtually lost in the modern horse.

Follow this by examining the reduction and loss of metacarpal V (red) and its digits (fingers). Do this likewise for metacarpals II (orange) and IV (green). Note that no horse ever had a thumb (I).

Reduction and loss of side toes minimizes the weight at the extreme end of the foot. This reduces the torque, so the horse's limb may move faster.