The Scapula and its Muscles

7. Deltoid and Latissimus Dorsi

The deltoid covers the rounded corner of the shoulder. It originates from the lateral third of the clavicle and scapula spine, specifically from the acromion process and the spi of the shoulder blade. It moves by pulling the humerus toward the acromion and is responsible for helping the arm extend backward, such as when athletes throw and execute underhand pitches. While the latissimus dorsi has some fibers that come from the scapula, it originates at the T7 vertebrae, which is also the tip of the trapezius muscle, and ends in the sacral region at the base of the spine. It depresses the scapula, particularly when supporting the full body during a pull-up.