The serratus posterior inferior is a muscle within the intermediate compartment of the back. It lies deep to the latissimus dorsi muscle in the lower back.
- Attachments: Originates from the thoracis and lumbar spines (usually T11 – L3) with the muscle fibres running in a superolateral direction, attaching to ribs 9 – 12.
- Actions: Depresses ribs 9 – 12.
- Innervation: Intercostal nerves (T9 – T11) and subcostal nerve (T12).
- Blood Supply: Supplied by the posterior intercostal arteries, subcostal artery, and upper lumbar arteries.