The past few days I've been trying to learn how to draw horses. Horses are not easy to draw, so I've been spending some quality time doodling in my notebooks (an example is below). Frequently I have annotated these doodles with notes on what is incorrect (I often don't make my horses long enough). Horses (and other hoofed animals) have an odd bone structure that makes their legs a little less than intuitive when drawing. Essentially they have one extra major joint, which occurs because their hooves are like the tips of their fingers, and their 'wrist' is what appears to be their front knee (also odd is that they have knees below their elbows).
To show what's going on inside, I drew a horse with the bone structure showing through the skin (bones not quite to scale). The horse limbs have 5 big zig-zags compared to the 4 in humans.