dstears:

How to Pony: Part 3 - Hind legs

Part1 , Part2

The hind legs still give me the most trouble. Their distinct shape means you can’t as easily treat them like a big noodle or a human appendage.  Hopefully the examples above will help understand how the shape deforms based on the pose. When in doubt, look for references and try to map them onto a pony form.

(Link to non-blurry dA version)

You should definitely check out this tutorial which explains the structure of the hind legs:
https://fargonon.deviantart.com/art/Fargo-s-Equine-Leg-Tutorial-638850747