The deltoid muscle is a triangular muscle that covers the shoulder joint. It is divided into three heads: anterior, middle, and posterior. The three heads of the deltoid muscle work together to lift the arm away from the body.
The anterior head of the deltoid muscle is the largest and strongest of the three heads. It originates on the clavicle and inserts on the humerus. The middle head of the deltoid muscle originates on the acromion and inserts on the humerus. The posterior head of the deltoid muscle originates on the spine of the scapula and inserts on the humerus.
All three heads of the deltoid muscle are important for shoulder movement. The anterior head lifts the arm forward, while the middle head lifts it to the side.
