The trachealis muscle is a thick band of smooth muscle that bridges the ends of each of the horseshoe-shaped cartilage rings that help to stabilize the entire length of the windpipe. The windpipe or trachea is a long slender tube that transports air to and from the lungs. A series of 16 to 20 horseshoe-shaped rings comprised of cartilage are distributed at various intervals down the length of the tube. The rings provide structural support and prevent the flexible tube from collapsing on itself. The gap in each ring is bridged by a combination of elastic connective tissue and smooth muscle termed trachealis muscle. The muscle fibers help adjust the flow of air into the lungs by either expanding or contracting.