Describe the origins of the deltoid’s clavicular, acromial, and spinal portions, its insertion, and the actions of each portion.

• A. Origins: anterior (clavicle) from the clavicle; middle from the acromion; posterior from the spine of the scapula. Insertion: deltoid tuberosity of the humerus. Actions: anterior fibers flex and medially rotate; middle fibers abduct; posterior fibers extend and laterally rotate.
• B. Origins: clavicular, acromial, and spinal from the clavicle, scapula, and humerus. Insertion: greater tubercle. Actions: abduction.
• C. Origins: from the scapula; Insertion: deltoid tuberosity; Actions: flexion only.
• D. Origins: from the humerus; Insertion: clavicle; Actions: rotation.

Answer: (A)

The key idea is that the deltoid is a three-headed muscle with distinct origins, all converging on a common insertion, and each head produces different shoulder movements. The clavicular part arises from the lateral third of the clavicle, the acromial part from the acromion, and the spinal part from the spine of the scapula. All three heads insert at the deltoid tuberosity on the lateral humerus. Because each head pulls in a different direction, they generate specific actions: the clavicular (anterior) fibers flex and medially rotate the arm; the acromial (middle) fibers are the primary abductors of the arm once movement begins (with the initial 15 degrees aided by supraspinatus); and the spinal (posterior) fibers extend the arm and laterally rotate it. Other options misstate either the origins, the insertion, or the actions—for example, placing the origin on the humerus or the insertion at the greater tubercle, or claiming the action is flexion only. The described pattern—three origins on the clavicle and scapula, insertion at the deltoid tuberosity, and distinct actions for each part—matches the textbook anatomy.