Lumbar square muscle anatomy: The lumbar square muscle maintains the upper body posture. Origin: medial one-half of the last rib; transverse process of 1 to 4 lumbar vertebrae. Via: through the iliolumbar ligament. Stopping point: approximately 5 cm of the medial lip of the superior iliac crest. Variations: 1 to 2 variations in the number of lumbar transverse processes attached; variation in the extent of the last rib attached. The lumbar square muscle is divided into three bundles: 1. Iliac rib bundle: links the ilium and the rib cage. 2, Iliopsoas bundle: links the ilium and lumbar transverse processes. 3.Lumbar rib bundle: linking the ribs and lumbar transverse process. Function and significance: 1. unilateral contraction – lateral flexion 2. unilateral contraction – lifting the pelvis 3. bilateral contraction – posterior extension of the spine (jerking the waist) 4. fixing the twelfth rib to assist in strenuous breathing 5. Stabilize the upper body posture 6. Stabilize the pelvic position