The below series of photographs use McGregor Museum specimens to illustrate the ancestral similarities (synapomorphies) and derived differences (apomorphies) between the hind leg of different quadrupedal mammals. Keep in mind the habit and locomotory behaviour of these animals as you compare their limb structure.
Here the leg of a goat (Capra aegagrus) represents the unguligrade anatomy of locomotion.
Likewise, the hind leg of the leopard (Panthera pardus; left) and european hare (Lepus europaeus; right) illustrate the digitigrade’s anatomy.
The above black bear (Ursus americanus) hind limb is representative of plantigrades anatomy.