Which muscle inserts on the inferior border of the 12th rib and transverse processes of L1-L4?

Which muscle inserts on the inferior border of the 12th rib and transverse processes of L1-L4?

• A. Longissimus thoracis
• B. Spinalis cervicis
• C. Quadratus lumborum
• D. Rectus abdominis

Answer: (C)

The key idea here is matching a muscle’s insertion with its actions. The muscle that inserts on the inferior border of the 12th rib and on the transverse processes of L1–L4 is the quadratus lumborum. Its attachment to the lower rib and those lumbar transverse processes lets it depress the 12th rib and bend the spine to the side, while also helping stabilize the lumbar spine and assist with deep, forced breathing by fixing the last rib during expiration. Other muscles don’t fit that exact insertion pattern: the longissimus thoracis runs along the thoracic region attaching to ribs and vertebrae but not specifically the inferior border of the 12th rib with L1–L4 transverse processes; the spinalis cervicis is located in the neck region; and the rectus abdominis runs from the pubic region to the costal cartilages of the lower ribs, not involving the 12th rib and L1–L4 transverse processes.

The key idea here is matching a muscle’s insertion with its actions. The muscle that inserts on the inferior border of the 12th rib and on the transverse processes of L1–L4 is the quadratus lumborum. Its attachment to the lower rib and those lumbar transverse processes lets it depress the 12th rib and bend the spine to the side, while also helping stabilize the lumbar spine and assist with deep, forced breathing by fixing the last rib during expiration.

Other muscles don’t fit that exact insertion pattern: the longissimus thoracis runs along the thoracic region attaching to ribs and vertebrae but not specifically the inferior border of the 12th rib with L1–L4 transverse processes; the spinalis cervicis is located in the neck region; and the rectus abdominis runs from the pubic region to the costal cartilages of the lower ribs, not involving the 12th rib and L1–L4 transverse processes.