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the muscles between adjacent ribs. They are designated as external and internal and function as secondary ventilatory muscles.
intercostal muscles Voluntary muscles, situated between each pair of adjacent ribs, which, on contracting, raise the rib cage upwards and outwards so as to increase the volume of the chest and cause air to be forced in by atmospheric pressure.
intercostal muscles the muscles lying between the ribs of vertebrates that, with the ribs, form the walls of the thorax. Contraction of external intercostal muscles brings about rib movement upward and outward, thus expanding the thoracic cavity reducing the thoracic pressure and drawing air into the lungs. see BREATHING.