Which muscle is responsible for depression of the ribs?

The intercostal muscles are essential to respiratory movements, including the depression of the ribs. These muscles are located between the ribs and assist in the mechanical aspect of breathing by controlling the movement and spacing of the ribs. During forced expiration, such as when coughing or exhaling forcefully, the intercostal muscles contract to pull the ribs downwards and inwards, thus decreasing the volume of the thoracic cavity and pushing air out of the lungs.

In contrast, the pelvic tilt relates to the position of the pelvis rather than rib movement. The quadratus lumborum is primarily involved in lateral bending of the lumbar spine and stabilization, while the quadriceps are knee extensors and play no role in rib movement. Therefore, the intercostal muscles are the correct choice for their direct involvement in the depression of the ribs during the breathing process.