Muscles at the top of the arm, just below the shoulder, responsible for shoulder motions in the front, side and back.

a muscle with origin from the lateral third of the clavicle, the lateral border of acromion process, and the lower border of spine of scapula, with insertion to the side of the shaft of the humerus, with nerve supply from the axillary nerve from the fifth and sixth cervical nerves through the brachial plexus, and whose action causes the abduction, flexion, extension, and rotation of the arm.

The deltoid muscle is the muscle forming the rounded contour of the human shoulder.