From Draw Like da Vinci: Leonardo's understanding of the facial muscles enabled him to create convincing expressions from a serene smile, to digust, contempt and anger. The intricate flat facial muscles pull between bones and skin. They are responsible for the infinite variety in facial expression. The eye and mouth are surrounded by broad bands of circular muscles; others pull parts of the face in many directions, such as elevating or depressing the corners of the mouth, the nostrils and forehead.