Detailed investigation on cleavage lines over the entire area of the body was undertaken in 3 each of male and female cadavers. The directions of cleavage lines showed sex and individual differences. Minute comparison of the diagrams obtained in this study with earlier diagrams revealed the presence of delicate differences in the directions of cleavage lines. Microscopical evaluation of cleavage lines showed that in the regions where cleavage lines were linearly arranged, collagen fibers were regularly arranged in a uniform direction, conforming to the direction of cleavage lines from the shallow reticular layer immediately below the papillary layers to the inner reticular layer where sebaceous and sweat glands existed and that in the regions where cleavage lines were ramified, collagen fibers in these layers lacked directional regularity. The morphology of cleavage lines were considered most influenced by collagen fibers in the epidermal reticular layers from their shallow layers immediately below the papillary layers to the layer where sebaceous and sweat glands existed.