The quadratus lumborum is a muscle of the posterior abdominal wall. It is a thick muscular sheet, quadrilateral in shape, and positioned superficial to the psoas major. Attachments: Originates from the iliac crest and iliolumbar ligament. The fibres travel superomedially, inserting onto the transverse processes of L1 – L4 and the inferior border of the 12th rib. Actions: Extension and lateral flexion of the vertebral column. It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is more efficient. Innervation: Anterior rami of T12 – L4 nerves. Blood supply: Lumbar, median sacral, iliolumbar and subcostal arteries. By TeachMeSeries Ltd (2025) Fig 1The quadratus lumborum of the posterior abdominal wall. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Print Article Rate This Article