How does the serratus anterior function as an antagonist to the rhomboid muscles?

Answer: Serratus anterior abducts the scapula and rhomboids adducts the scapula.

Serratus anterior is a muscle that originates of the 1st to 8th ribs at the side of the thorax and inserts in the medial border of the scapula. This muscle during contraction abducts the scapula and the rhomboids muscles do the opposite by retracting the scapula toward the vertebral column (adducts).