Trachea, section of the mammalian respiratory tract in the neck, extending between the larynx and the bronchi and lying in front of the esophagus. The trachea, commonly called windpipe, is made up of numerous cartilaginous half-rings, the open ends of which are adjacent to the esophagus. These rings, located one above the other, are connected by muscular and fibrous tissue. The trachea in humans is about 10 cm (4.5 in) long and 2.5 cm (1 in) in diameter. It is lined internally with a ciliated mucous membrane. The trachea is highly susceptible to respiratory infections. A tracheotomy, the surgical opening of the trachea, may be necessary if the tube is obstructed by a foreign object or because of a disease. The air tubes of certain insects are also called tracheae. See Respiration.