Chambon

A chambon is a piece of horse tack. It is a strap that runs forward from the bottom of the girth or surcingle, and forks. The forks continue to a ring on either side of the bridle or halter, at the base of the crownpiece. Running through those rings, the forks follow the cheekpieces to the bit. They may attach to the bit or pass through the bit rings and attach to themselves below the horse's neck.

A chambon prevents the horse from raising its head beyond a fixed point. Raising the head causes the length of the chambon along the cheekpieces to shorten and thus puts reciprocal pressure on the horse's mouth and on the horse's poll. Horses generally dislike pressure behind the poll and learn to release the pressure by lowering their head, and when in motion, this encourages the horse to relax its back and bring its hindquarters further under its body, thus encouraging collection. The chambon has the opposite function to an overcheck or bearing rein, which is used to raise the horse's head. Provided by Wikipedia