The origin of the deltoid includes which structures?

• A. Medial 1/3 of clavicle
• B. Lateral 1/3 of clavicle, acromion, and spine of scapula
• C. Inferior angle of scapula
• D. Coracoid process

Answer: (B)

The deltoid has three distinct origins that form its broad shape around the shoulder: the lateral third of the clavicle, the acromion, and the spine of the scapula. This arrangement supports its multi-directional function: the clavicular part helps with shoulder flexion and internal rotation, the middle part is the primary contributor to abduction, and the spinal part assists with extension and external rotation. All fibers converge on the deltoid tuberosity of the humerus, so contracting from these three points allows the arm to be lifted in various directions. The other landmarks mentioned are associated with different muscles—for example, the medial clavicle is a typical origin for pectoralis major; the inferior angle of the scapula is linked to teres major; and the coracoid process serves as the origin for coracobrachialis, pectoralis minor, and the short head of biceps.