Serratus anterior m.

The serratus anterior is a muscle that originates in multiple small bellies on the surface of the 1st to 8th ribs at the side of the chest. It passes posteriorly between the ribs and the scapula (deep to the latissimus dorsi m.) and inserts along the entire length of the anterior surface of the medial border of the scapula.

The serratus anterior is innervated by the long thoracic n., which travels inferiorly on the external surface of the serratus anterior. The nerve is especially vulnerable during certain types of surgery (e.g., axillary dissection to remove cancerous lymph nodes in breast cancer). Damage to this nerve can lead to a winged scapula.

Although it serves other functions as well, the serratus anterior is a major protractor of the scapula. It is sometimes called the "big swing muscle" or the "boxer's muscle" because protraction of the scapula forward and around the rib cage occurs when swinging or extending your arm anteriorly, as in throwing a punch.