Final answer:
When the humerus is fixed, contraction of the latissimus dorsi muscle fibers that insert into the lower ribs will pull the lower ribs towards the humerus, causing inferior rotation of the ribs.
Step-by-step explanation:
When the humerus is fixed in position, contraction of the fibers of the latissimus dorsi muscle that insert into the lower ribs will pull the lower ribs towards the humerus. This movement is called inferior rotation of the ribs. The latissimus dorsi muscle is responsible for several movements of the arm and shoulder, including adduction, extension, and medial rotation of the arm.