Which muscle protracts the shoulder and rotates the glenoid cavity superiorly when the scapula is fixed?

• A. Serratus Anterior
• B. Latissimus Dorsi
• C. Subscapularis
• D. Frontalis

Answer: (A)

Protracting the shoulder blade and upwardly rotating the glenoid cavity when the scapula is fixed is the job of the serratus anterior. This muscle attaches to the ribs and the medial border of the scapula; when it contracts, it pulls the scapula forward along the rib cage (protraction) and rotates the scapula so the glenoid cavity tilts upward. That upward rotation is what allows the arm to be raised and the shoulder to move efficiently through a full range of motion. The other muscles listed don’t produce this combination: latissimus dorsi mainly moves the arm itself (extension, adduction, internal rotation) rather than the scapula; subscapularis is a rotator cuff muscle that medially rotates and stabilizes the humerus; and the frontalis is a facial muscle with no role in shoulder girdle movement.