Which muscle inserts on the inferior border of ribs 8-12?

Which muscle inserts on the inferior border of ribs 8-12?

• A. Serratus posterior inferior
• B. Serratus posterior superior
• C. Levator scapulae
• D. Trapezius

Answer: (A)

Understanding where a back muscle attaches helps explain its job. The serratus posterior inferior originates from the lower thoracic and upper lumbar spine and thoracolumbar fascia, then inserts along the inferior borders of ribs 8 through 12. This placement lets it pull the lower ribs downward during expiration, stabilizing the ribcage. It’s innervated by the thoracic intercostal nerves. The other muscles mentioned attach to different structures—serratus posterior superior goes to the superior borders of ribs 2–5; levator scapulae attaches to the scapula; trapezius attaches to the clavicle and the spine/acro­mion of the scapula—so they don’t insert on the inferior borders of ribs 8–12.

Understanding where a back muscle attaches helps explain its job. The serratus posterior inferior originates from the lower thoracic and upper lumbar spine and thoracolumbar fascia, then inserts along the inferior borders of ribs 8 through 12. This placement lets it pull the lower ribs downward during expiration, stabilizing the ribcage. It’s innervated by the thoracic intercostal nerves. The other muscles mentioned attach to different structures—serratus posterior superior goes to the superior borders of ribs 2–5; levator scapulae attaches to the scapula; trapezius attaches to the clavicle and the spine/acro­mion of the scapula—so they don’t insert on the inferior borders of ribs 8–12.