The galea aponeurotica is a muscle that covers the upper part of the cranium (skull). Its attachment to the frontal and occipital bellies (muscles on the brow at the front and on the upper back of the head) allows it to move the scalp freely over the underlying skull bone. The occipital and frontal bellies work together with this muscle to draw back the scalp, raise the eyebrows, and wrinkle the foreheadmycontentbreak in an expression of surprise.