The winged scapula results from a lesion of the long thoracic nerve, which supplies the serratus anterior muscle. This muscle is responsible for rotating the scapula upward, which occurs during abduction of the arm above the horizontal. The long thoracic nerve comes off the C5 to C7 roots of the brachial plexus. The diaphragm is supplied by the phrenic nerve, which comes off the spinal nerve roots C3 to C5.