The muscle lies at the junction of the thoracic and lumbar regions. The origin arises from the vertebrae T11 through L2. The muscle's insertion is the lower border of the 9th through 12thribs.
It is situated at the junction of the thoracic and lumbar regions: it is of an irregularly quadrilateral form, broader than the serratus posterior superior muscle, and separated from it by a wide interval.
The serratus posterior inferior draws the lower ribs backward and downward to assist in rotation and extension of the trunk. This movement of the ribs also contributes to forced expiration of air from the lungs.