Ultrastructure of the Human Toenail I. Proximal Nail Matrix

Electron microscopic examination of the proximal matrix of the human toenail revealed that the proximal end was branched into a few to several rootlets. It was composed of essentially the same dorsal, apical and ventral portions in which active melanocytes, Langerhans' cells and a Merkel cell were found. The basal matrix cells had finger-like cytoplasmic projections into the surrounding mesoderm. Bundles of fine fibrils (“anchoring bundles”) streamed down from the basal lamina, particularly from the basal lamina covering the finger-like projections. Numerous slender villi, developed from the peripheral cytoplasm, rightly interlocked the basal matrix cells. Cell-to-cell junctions became rather loose as the basal cells left the basal layer. Melanosomes of melanocytes were not well developed in Caucasian nail matrix, some were well developed in the Japanese nail and usually fully melanized in the Negro nail. Only one Merkel cell was encountered. It contained dense, membrane-surrounded secretory granules and was connected to the neighboring keratinocytes with desmosomes