Final answer:
The deltoid muscle opposes the pectoralis major and latissimus dorsi in terms of arm abduction and adduction.
Step-by-step explanation:
In terms of adduction and abduction of the arm, the muscle that opposes the pectoralis major and latissimus dorsi is the deltoid. The pectoralis major is a thick and fan-shaped muscle that covers the superior portion of the anterior thorax and assists in adducting the arm.
The latissimus dorsi is a broad, triangular muscle located on the inferior part of the back, also involved in adducting the arm. On the other hand, the deltoid is the major abductor of the arm, facilitating abduction as well as different movements such as flexing and medial rotation, and extension and lateral rotation of the arm.