In humans, the pectoral girdle, or shoulder girdle, is made up of the scapula, clavicle and various muscle groups. It functions by connecting the upper limb to the spinal column through a series of muscles in the shoulder and upper back.
The long, upper bone in the arm, called the humerus, fits into the scapula via a depression called the glenoid cavity. Unlike the pelvic girdle, the pectoral girdle relies on muscular connections to hold it into place, rather than a physical joint structure. The rhomboids, trapezius and levator scapulae muscles attach the upper part of the pectoral girdle to the axis of the body. The serratus anterior, located underneath the armpit, holds the girdle into place by attaching to the ribcage.
Since the pectoral girdle is held in place by muscles only, it has a much wider range of motion than the pelvic girdle, but the pectoral girdle is much weaker as a result. The skeletal connections and ligaments of the pelvic girdle are much more stable, resulting in increased stability and strength. In humans, the pelvic girdle consists of two bones, but in some mammalian species there are three. The third bone is called a coracoid. The pectoral girdle is unique because its structure varies widely between animal species.