The function of the cartilaginous rings of the trachea is to stabilize the trachea and keep it rigid while allowing the trachea to expand and lengthen when the person breathes. If the trachea was not supported in this way, it would simply collapse because of the pressure of the chest. There are between 16 and 20 cartilaginous rings in an average trachea.
The cartilage rings are C-shaped because the back of the trachea presses against the esophagus. The cartilage opens at the esophagus and is replaced by connective tissue and muscle. This gives the esophagus space to allow food to be swallowed easily.
The rings of the trachea are stacked one on top of the other, with a small space between them. They're thicker in the middle than they are at the edges. Each one is about 0.16 inches deep and 0.039 inches thick. The trachea itself is only about 4 to 6 inches long.
The first and last tracheal rings are broader and deeper than the others. The first ring is just beneath the larynx and the thyroid gland. The last one is just above where the trachea branches off into the bronchi, the two tubes that lead to the lungs.