What attachment site do the trapezius and deltoid muscles have in common?

• A. Acromion
• B. Coracoid process
• C. Spine of scapula
• D. Lateral clavicle

Answer: (A)

Both trapezius and deltoid anchor to the acromion, a bony projection on the scapula. The trapezius attaches to the acromion as part of its scapular attachments, while the deltoid originates from the acromion (as well as the lateral clavicle and spine of the scapula) and then inserts on the humerus. This shared acromial attachment lets these two muscles link across the shoulder girdle and influence scapular and shoulder movements. The coracoid process isn’t a shared site for these two, which helps explain why acromion is the common attachment listed.