Serratus Posterior Inferior

Joe Muscolino

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  • The serratus posterior inferior attaches from the spinous processes of T11-L2 to ribs 9 through 12.



  • The serratus posterior inferior depresses ribs 9 through 12 at the sternocostal and costospinal joints.
  • Note: Generally muscles that depress ribs act to create expiration. But a muscle that depresses the lower ribs could act to stabilize the lower ribs against the upward pull of the diaphragm, thereby assisting the diaphragm’s dome to drop (increasing the vertical diameter of the thoracic cavity to allow for expansion of the lungs), thereby acting to assist with inspiration.