Deltoid

The deltoid m. forms the rounded contour of the shoulder, and is one of the main muscles that acts to move the arm at the shoulder joint.  It has a broad area of origination, from the lateral clavicle, acromion process and spine of the scapula.  It inserts into the humerus at the deltoid tuberosity.  The deltoid m. is a strong abductor at the shoulder, and also extends and flexes the arm at the shoulder.  It’s innervation is the axillary n.