This illustration shows the respiratory tracts with the larynx, trachea, and lung. In the middle, the larynx is visible with the thyroid and its cricoid cartilage. The trachea that branches into left and right principal bronchus follows next. The principal bronchi branch into two and three secondary bronchi and the lap bronchi split into tertiary bronchi as you can see on the right side of the illustration. On the left: lung and its separation into top, middle and bottom lap by oblique and horizontal fissure.