Familiarity with lacrimal system embryology is necessary to understand congenital abnormalities of the nasolacrimal drainage system. The orbital walls are embryologically derived from neural crest cells. Ossifi cation of the orbital walls is completed by birth except at the orbital apex. The lesser wing of the sphenoid is initially cartilaginous, unlike the greater wing of the sphenoid and other orbital bones that develop via intramembranous ossifi cation. The membranous bones surrounding the lacrimal excretory system are well developed at 4 months of embryologic age and ossify by birth
