Anatomical and microscopic study of the volar dermal ridges of the rat (Rattus norvegicus).

The epidermal ridges of the rat (Rattus norvegicus), which are distributed only on the volar pads and digital apices, were studied. Examination of the ridges was difficult on the epidermal surface, as the undulations expressed on the epidermis are weak. Therefore, the dermal surface, prepared by alkaline solution treatment, was inspected by scanning electron microscopy and staining with toluidine blue. The dermis of the pads and digital apices is composed of ridged and rippled areas. The ridged area, where sweat ducts are distributed, is constructed of grooves and ramparts. Frequently, the sweat duct is surrounded by a dermal collar, and the groove is separated by a dermal partition. The grooves and ramparts display dermatoglyphic configurations, such as whorls, loops, cusps, triradii, and some other patterns, which are peculiar to each pad and digital apex and comparable to dermatoglyphic patterns of man and other primates.