Deltoid muscle

The deltoid muscle is a large muscle that lies over the shoulder and is responsible for the lateral movement of the arm.

The deltoid muscle has a front, side and middle area, covering the most of the top of arm where it meets the torso. The anterior portion of the muscle originates at the acromion process of the scapula (shoulder blade), and extends to the distal area of the humerus (upper arm bone). The deltoid is innervated by a group of nerves in the cervical area of the spine.

Origin
The deltoid muscle originates from the clavicle and the scapula. It attaches to the lateral third of the clavicle. On the scapula, it attaches to the acromion process, and the spine of the scapula.

Insertion
The deltoid muscle inserts at the middle of the lateral surface of the humerus. This attachment point is called the deltoid tuberosity.

Word origin
The deltoid muscle is named for the Greek letter delta (Δ), as both have a triangular shape.