Final answer:
The serratus anterior has a "serrated" appearance because it is attached to the ribs, and is involved in scapular movement and arm rotation.
Step-by-step explanation:
The serratus anterior muscle has a "serrated" appearance due to its attachment to the ribs. This large and flat muscle originates on the lateral sides of the ribs and inserts onto the medial border of the scapula, playing a crucial role in the movement of the scapula and shoulder. It is responsible for allowing the forward rotation of the arm and pulling the scapula forward and downward.