Which muscle originates from the posterior iliac crest?

• A. Quadratus lumborum
• B. Rectus abdominis
• C. External oblique
• D. Diaphragm

Answer: (A)

Knowing where a muscle originates helps identify it. The posterior iliac crest is the back edge of the iliac bone, and the muscle that starts there is the quadratus lumborum. It also attaches to the 12th rib and the transverse processes of the upper lumbar vertebrae, which fits its role in stabilizing the spine and aiding lateral flexion and extension of the lumbar region. The other muscles have different starting points: the rectus abdominis begins at the pubic crest and symphysis; the external oblique from the lower ribs; the diaphragm from the xiphoid process, costal margins, and lumbar vertebrae. So the muscle originating from the posterior iliac crest is quadratus lumborum.