The key idea is where the muscle attaches to bone and how that supports its action. The triceps brachii inserts at the olecranon process of the ulna, which is the bony prominence at the tip of the elbow. When the triceps contracts, it pulls on the olecranon to extend the elbow, straightening the forearm. Why this site fits best: the olecranon serves as the leverage point for elbow extension, making it the natural insertion for an elbow extensor like the triceps. The other sites correspond to different muscles or actions (for example, the intertubercular groove is a humeral groove associated with the biceps and other muscles, the greater tubercle is a rotator cuff/fixed shoulder region, and the radial tuberosity is the insertion for the biceps on the radius).

Innervation of the rhomboid major comes from the dorsal scapular nerve, a branch of the C5 nerve root. This nerve travels to the deep surface of the rhomboid muscles and provides motor input that enables retraction and downward rotation of the scapula. The dorsal scapular nerve specifically targets the rhomboids (major and minor), which is why it’s the correct choice. The other nerves have different targets: the suprascapular nerve goes to the supraspinatus and infraspinatus, the axillary nerve to the deltoid and teres minor, and the long thoracic nerve to the serratus anterior.

The anterior part of the deltoid is oriented to move the arm forward and rotate it inward. Its fibers originate from the lateral clavicle and insert on the deltoid tuberosity, so their main action is shoulder flexion and medial (internal) rotation, with some help in horizontal adduction. The middle fibers do the primary abduction once the arm has cleared the initial range (the first ~15 degrees of abduction is driven by the supraspinatus). The posterior fibers extend the arm and rotate it laterally. So describing the anterior deltoid as flexing and medially rotating the arm accurately captures its main function.

The key idea is where a rotator cuff muscle attaches to the scapula and how that position shapes its action. Teres minor originates from the lateral border of the scapula, specifically the middle portion, on the posterior side, and it inserts into the greater tubercle of the humerus. That placement gives it a pull that assists external rotation of the shoulder and helps stabilize the humeral head in the glenoid, working alongside the infraspinatus. The other locations don’t fit because the medial border is the inner edge of the scapula (not where teres minor attaches), the inferior angle is the origin for teres major, and the anterior surface is where subscapularis originates.