Serratus anterior
Chest
- Origin
- Outer surfaces of ribs 1 to 8
- Insertion
- Medial border of the scapula (front surface)
- Action
- Protracts the scapula and rotates it upward
The saw-toothed muscle on the side of the rib cage. It keeps the shoulder blade flat against the ribs and lets the arm reach fully overhead; push-ups train it well.