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Internal intercostal muscles
Medical expert of the article
Last reviewed: 07.07.2025
The internal intercostal muscles (mm. intercostales interni) are located medially from the external intercostal muscles. They occupy the intercostal spaces, starting from the edge of the sternum (at the true ribs) and the anterior ends of the cartilages of the false ribs and to the angles of the ribs at the back, where their continuation is the internal intercostal membrane (membrane - membrana intercostalis interna). These muscles begin at the upper edge of the underlying rib and the corresponding costal cartilage and are attached to the lower edge of the overlying rib medially from the costal groove.
The bundles of internal intercostal muscles are directed obliquely from below upward and laterally at the posterior chest wall, and upward and medially at the anterior wall. The internal intercostal muscles are located at almost a right angle to the bundles of external intercostal muscles. The internal bundles of these muscles are called the innermost intercostal muscles (mm. intercostales intimi).
Function of the internal intercostal muscles: the internal intercostal muscles lower the ribs and strengthen the sternocostal joints.
Innervation of the internal intercostal muscles: intercostal nerves (ThI-ThXI).
Blood supply of the internal intercostal muscles: posterior intercostal arteries, intercostal branches of the internal thoracic artery, muscular-diaphragmatic artery.
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