Which of the following muscles adducts the arm?

The subscapularis muscle is indeed the one that primarily adducts the arm. This muscle is located on the anterior surface of the scapula and is one of the rotator cuff muscles. Its primary actions include internal rotation of the humerus and adduction of the arm. When the subscapularis contracts, it pulls the humerus towards the body, facilitating adduction.

The infraspinatus and teres minor are also rotator cuff muscles but they are primarily responsible for external rotation of the arm rather than adducting it. The supraspinatus plays a key role in the initial abduction of the arm rather than adduction.

Understanding the specific roles of these muscles in shoulder mechanics is crucial, particularly in the context of their contributions to movements like adduction, internal and external rotation, and abduction. This knowledge is essential for grasping the functional anatomy of the shoulder girdle in both healthy and pathological states.