In the present investigation an analysis has been made of the fine structure of the interrelationships of cells in human forearm epidermis by means of the electron microscope.

The "intercellular bridges," here called attachment zones, are more complex than has previously been recognized. It is shown that dense oval thickenings, called attachment plaques, appear in apposed areas of adjacent epidermal cell membranes. The tonofibrils terminate at the internal face of the attachment plaque and do not traverse the 300 A distance between apposed plaques. Seven intervening layers of unidentified substance occupy the space between attachment plaques. The attachment zones appear in all of the classical histological layers of the epidermis.

The portions of epidermal cell membrane not involved in intercellular attachments have extensive surface area resulting from plication of the membrane, and its further modification to form microvilli. The possible functional significance of these observations is discussed. Prior observations concerning the basement membrane of epidermis are confirmed.

Identification of epidermal melanocytes is achieved, the finer morphology of their dendritic processes is described, and their relationship to epidermal cells is discussed.

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