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External intercostal muscles
Last reviewed: 07.07.2025
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The external intercostal muscles (mm. intercostales externi), 11 on each side, originate at the lower edge of the overlying rib, outside of its groove, and, directed downward and forward, are attached to the upper edge of the underlying rib. The muscles occupy the intercostal spaces from the tubercles of the ribs at the back to the costal cartilages in front, where their continuation to the edge of the sternum is the external intercostal membrane (membrane - membrana intercostalis externa). On the back of the chest, the bundles of these muscles are oriented obliquely downward and laterally, on the lateral and anterior sides - downward, forward and medially. These muscles form a thicker layer compared to the internal intercostal muscles.
Function of the external intercostal muscles: they raise the ribs; their posterior parts strengthen the costovertebral joints.
Innervation of the external intercostal muscles: intercostal nerves (ThI-ThXI).
Blood supply of the external intercostal muscles: posterior intercostal arteries, anterior intercostal branches of the internal thoracic artery, musculophrenic artery.
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