Human Anatomy - Kotsan I. Y. 2009

Muscles and Fascia of the Trunk
Muscles of the Posterior Abdominal Wall

The posterior abdominal wall is formed by a single Muscle, the quadratus lumborum muscle (Figs. 99, 106).

The quadratus lumborum muscle (m. quadratus lumborum) is a flat, quadrilateral muscle. It is located posteriorly between the lumbar spine, the 12th rib, and the iliac crest. It originates from the inner lip of the iliac crest and the transverse processes of the lower lumbar vertebrae. It inserts into the body of the 12th thoracic vertebra, the 12th rib, and the transverse processes of the upper lumbar vertebrae. It is separated from the back Muscles by the Deep Layer of the thoracolumbar fascia. Function: pulls the twelfth rib downward and the iliac bone upward. When contracting unilaterally, it bends the spine to its respective side; when contracting bilaterally, it maintains the spine in an upright position.

Innervation: muscular Branches of the Lumbar plexus.



Last update: 08/08/2026

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