The external intercostal muscles (Musculi intercostales externi) occupy the intercostal spaces superficially from ventral extent of levator costarum to costochondral junction, and do not extend as far as the sternum like the internal intercostal muscles. The fibers of the external intercostal muscles are orientated perpendicular to the ones of the internal intercostal muscles.
Origin: lower border of ribs
Insertion: upper border of rib below
Action: inspiration, to draw the ribs together so as to enlarge the thoracic cavity
Nerve: Intercostal nerves one to twelve.