Straps attached to bit and held in rider's hands

Leather straps attached to the bridle to control and steer the horse.

Leather straps attached to the bridle by which the rider directs the horse.

the handles of tongs

The kidneys; also, the region of the kidneys; the loins.

The inward impulses; the affections and passions; -- so called because formerly supposed to have their seat in the part of the body where the kidneys are.

power to control; "the reins of government"