Enamel in longitudinal section of tooth - human, adult. Thin ground section.

From left to right: incremental lines (striae) of Retzius are distinctly shown as oblique broad zones (at the left) to the enamel surface; during formation of the crown successive apposition of layers of enamel is deposited and results in these so-called incremental grow lines; surface of enamel in cervical region; the parallel arrangement of stacks of rods (prisms) is evident.