Why are artiodactyls often called even-toed ungulates?

Artiodactyls are referred to as even-toed ungulates because they possess an even number of functional toes on each of their feet.1

This classification distinguishes them from perissodactyls, or odd-toed ungulates, which have an odd number of toes on their hind feet. While the specific number of toes can vary among artiodactyl species—for example, some have two toes, while others like hippopotamuses and chevrotains have four—the count is always even. In many two-toed species, the hooves appear split or "cloven," leading to the common description of these animals as cloven-hoofed.21