It usually refers to the assembly of components that contacts and controls the horses mouth, and includes the shanks, rings, cheekpads and mullen, all described here below, but it also sometimes simply refers to the mullen, the piece that fits inside the horse's mouth. The mullen extends across the horse's mouth and rests on the bars, the region between the incisors and molars where there are no teeth. The bit is located on the horse's head by the headstall, and which has itself several components to allow the most comfortable adjustment of bit location and control.