We call them fore legs and hind legs.

People have two pairs also.

We call them arms and legs.

So you see our arms correspond to the fore legs of beasts, though we never use them for moving about, except when we go on our hands and knees, or climb trees, or swim in the water.

And as for birds--why, their fore limbs are turned into wings, to fly with, so that they walk or hop on their hind limbs only, just as we do.