Serratus Posterior Inferior

Joe Muscolino

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The serratus posterior inferior bilaterally. The latissimus dorsi has been ghosted in on the left side.

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



  • The serratus posterior inferior depresses ribs 9-12 at the sternocostal and costospinal joints.



  1. There are two posterior serratus muscles: serratus posterior inferior and serratus posterior superior. There is one anterior serratus muscle: serratus anterior.
  2. 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.