Anatomy and embryology of the eyelids: a review with special reference to the development of divided nevi.

In this review of the basic anatomy and embryology of the human eyelids, the sequence of eyelid differentiation is discussed. The development is important in exploring the formation of divided or "kissing" nevi of the lids. Since the lids are fused from the ninth week until the twentieth week of gestation, one may propose that the precursor elements of the nevus develop during that specific time. Because the epithelium only is fused, melanocytes derived from the neural crest must begin their differentiation in the region of the fused epithelium.