It's important to note that the fetlock joint is not a single bump, but rather a complex articulation between several bones:
* Proximal phalanx (P1): The long pastern bone
* Middle phalanx (P2): The short pastern bone
* Sesamoid bones: Two small, round bones located behind the fetlock joint
The fetlock joint is responsible for flexing and extending the horse's pastern and allowing the horse to lift its foot off the ground. It's a crucial part of the horse's lower leg and is prone to injury.