Which muscle inserts at the last rib and transverse processes of L1-L4?

Which muscle inserts at the last rib and transverse processes of L1-L4?

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

Answer: (A)

Mapping muscle attachments helps you predict function. The muscle that inserts on the last rib and the transverse processes of L1–L4 is the quadratus lumborum. Its attachment to the 12th rib and to the transverse processes of the first four lumbar vertebrae lets it stabilize the lumbar spine and contribute to lateral flexion of the trunk, as well as assist in depressing the 12th rib during deep or forced breathing. The other muscles listed have different insertion patterns: the diaphragm attaches to the central tendon and rib margins, the external oblique attaches along the iliac crest and the abdominal aponeurosis with the lower ribs, and the rectus abdominis attaches to the pubic bone and the costal cartilages of the upper ribs. So the described insertion matches quadratus lumborum.

Mapping muscle attachments helps you predict function. The muscle that inserts on the last rib and the transverse processes of L1–L4 is the quadratus lumborum. Its attachment to the 12th rib and to the transverse processes of the first four lumbar vertebrae lets it stabilize the lumbar spine and contribute to lateral flexion of the trunk, as well as assist in depressing the 12th rib during deep or forced breathing. The other muscles listed have different insertion patterns: the diaphragm attaches to the central tendon and rib margins, the external oblique attaches along the iliac crest and the abdominal aponeurosis with the lower ribs, and the rectus abdominis attaches to the pubic bone and the costal cartilages of the upper ribs. So the described insertion matches quadratus lumborum.