Real-time left The<unk>  is the main muscle of respiration and functions in breathing. During inhalation, the<unk>  contracts and moves in the inferior direction, enlarging the volume of the<unk>  cavity and reducing intra-thoracic pressure (the external intercostal muscles also participate in this enlargement), forcing the lungs to expand. In other words, the<unk> 's movement downwards creates a partial vacuum in the<unk>  cavity, which forces the lungs to expand to fill the void, drawing air in the process. Cavity expansion happens in two extremes, along with intermediary forms. When the lower ribs are stabilized and the central tendon of the<unk>  is mobile, a contraction brings the insertion (central tendon) towards the origins and pushes the lower cavity towards the pelvis, allowing the<unk>  cavity to expand downward. This is often called belly breathing. When the central tendon is stabilized and the lower ribs are mobile, a contraction lifts the origins (ribs) up towards the insertion (central tendon) which works in conjunction with other muscles to allow the ribs to slide and the<unk>  cavity to expand laterally and upwards. When the<unk>  relaxes (moves in the superior direction), air is exhaled by elastic recoil process of the lung and the tissues lining the<unk>  cavity. Assisting this function with muscular effort (called forced exhalation) involves the internal intercostal muscles used in conjunction with the abdominal muscles, which act as an antagonist paired with the<unk> 's contraction. The<unk>  is also involved in non-respiratory functions. It helps to expel vomit, feces, and urine from the body by increasing intra-abdominal pressure, aids in childbirth, and prevents acid reflux by exerting pressure on the esophagus as it passes through the esophageal hiatus. In some non-human animals, the<unk>  is not crucial for breathing; a cow, for instance, can survive fairly asymptomatically with<unk> atic paralysis as long as no massive aerobic metabolic demands are made of it.
Thoracic diaphragm
Diaphragm 
Thoracic inlet
Boracic lint
Cervical rib
Subclavian loop
Pleural cavity
Lung cavity