The cellular envelope of the human toenail cell becomes twice as thick as the original cell membrane of the matrix cell. It was found that this thickened envelope, ie, the marginal band, was not formed by the coating of the original cell membrane by discharged contents of the membrane coating granules (MCGs). Instead, it was produced by the precipitation of proteinaceous material on the cytoplasmic side of the cell membrane. Keratohyaline granules do not seem to contribute to the formation of the marginal band, since the nail cells keratinized by accretion of tonofibrils without the formation of keratohyaline granules.
Hashimoto K. The Marginal BandA Demonstration of the Thickened Cellular Envelope of the Human Nail Cell With the Aid of Lanthanum Staining. Arch Dermatol. 1971;103(4):387-393. doi:10.1001/archderm.1971.04000160037006