Serratus anterior muscle

The serratus anterior muscle is a muscle of the chest that connects the top eight ribs to the scapula (shoulder blade). When contracted, it brings the scapula forward, moving the shoulder in a punching motion.

Origin
The serratus anterior originates from the upper eight ribs. At the attachment to ribs 5 through 8, it is interdigitated with the external oblique muscle.

Insertion
The serratus anterior inserts along the anterior surface of the scapula at the inner medial border. The part of the muscle that originates from the first and second rib inserts at the upper angle of the scapula. The part that originates from the third and fourth rib inserts along the length of the costal surface. The part that originates from the fifth through eighth ribs inserts at the inferior angle.

Innervation
The serratus anterior is innervated by the long thoracic nerve (C5-C7).

Word origin
Serratus means saw tooth, in the same way as in serrated knife, referring to the back-and-forth pattern the muscle makes as it attaches to each rib.  Anterior , meaning on the front side, distinguishes it from the two serratus posterior muscles located on the back of the rib cage.