Pelvic girdle attaches to several postural muscles. Also, muscles pertaining to respiration take their origin on the pelvic girdle. Breathing refers to the mechanical process of moving air into and out of the lungs. It also is the mechanical process for generating sound into the upper aspect of the respiratory tract. 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.