Fig. 6. Lacrimal drainage system embryology. A. At 5.5 weeks' gestation, an ectodermal invagination forms between the lateral nasal process and maxillary process, which becomes pinched off from the surface. B. At 6 weeks' gestation, a solid cord of ectoderm is located between the primitive medial canthus and nose. C. At 12 weeks' gestation, proliferation of the cord occurs laterally toward the eyelid and inferiorly toward the inferior turbinate. The isolated cavities shown appear at 3 to 4 months. D. At 7 months, canalization is nearly complete, with only the puncta and valve of Henle remaining imperforate. (Doxanas MT, Anderson RL: Clinical Orbital Anatomy, p 9. Baltimore, Williams & Wilkins, 1984)