suffrago

from The Century Dictionary.

• noun The hock, or so-called knee, of a horse's hind leg, whose convexity is backward, and which corresponds to the human heel; the tibiotarsal articulation. See cuts under hock and Perissodactyla.
• noun In ornithology, the heel proper, sometimes called the knee; the mediotarsal articulation, whose convexity is backward, at the top of the shank, where the feathers of most birds stop.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) The heel joint.