The rings hold the trachea open. Posterior wall has trachealis muscle to fill the gap between the C-rings. The trachea extends superiorly to cricoid cartilage of the larynx. Trachea lined inside with ciliated epithelial mucous membrane. Mucous glands secrete mucus to moisten incoming air and move particles out of the trachea with its sweeping cilia.
Vocalization is secondary use of the respiratory tract.
Much coordination between musculature is necessary for both respiration and breathing. They are highly elastic. Color at birth is white to pinkish white. With age they darken because of contamination from the atmosphere. Apex of each lung points upward and fits into a space bounded by upper ribs, sternum and vertebrae.