Serratus anterior muscle

The serratus anterior is a muscle that originates on the surface of the upper eight ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula.

Function
The serratus anterior is occasionally called the "boxer's muscle" because it is largely responsible for the protraction of the scapula--that is, the pulling of the scapula forward and around the rib cage that occurs when someone throws a punch. The serratus anterior also helps to stabilize the scapula. In addition, it assists in rotating the scapula (glenoid fossa) upward.

Innervation
The serratus anterior is innervated by the long thoracic nerve, a branch of the brachial plexus. The long thoracic nerve travels inferiorly on the surface of the serratus. The nerve is especially vulnerable during certain types of surgery (for example, during lymph node clearance from the axilla). See winged scapula for more details.