From seven to eight the pinchers are noticeably worn; from eight to nine the middle pairs, and by ten years the corner teeth. After 6 years the arch gradually loses its rounded contour and becomes nearly straight by the twelfth year. In the meantime the teeth have gradually become triangular in shape, distinctly separated, and show the progressive wearing to stubs. [Illustration: FIG 6.--Internal face of incisors at 12 years.]