The Serratus Anterior is a broad, flattened muscle that runs from the lateral surface of the ribs, passes posteriorly around the thoracic wall, and inserts on the costal surface of the medial border of the scapula. You can feel this muscle by putting your hand just underneath your armpit. The function of this muscle is to allow for forward elevation of the arm and to pull the scapula forward around the rib cage (protraction). Due to its large role in stabilizing the scapula as well as contributing to overall shoulder health, when weakness is present, it often manifests with either scapular winging or poor scapular control.