Development of dermal ridges in the volar skin of fetal pigtailed macaques (Macaca nemestrina)

Development of the dermal ridges in volar skin was investigated in 28 pigtailed macaque (Macaca nemestrina) fetuses of known gestational age, ranging from 51 days postconception to newborn. Histology, scanning electron microscopy, and staining of the abraded dermal surface were used in the study. Morphological features of the dermal-epidermal system and their changes with advancing age are described. Chronology was established for stages in the development of the volar skin, i.e., the differentiation of the primary and secondary epidermal ridges (PER and SER) at the undersurface of the epidermis corresponding to the formation of primary and secondary dermal ridges (PDR and SDR) and the development of the dermal papillae. PDRs were first seen at 55 gestational days and SDRs at 93 days. Differentiation of sweat ducts occurred over the period between 60 and 119 gestational days. A regional sequence of differentiation starting with the digital apices of the hand and ending in the calcar area and the phalanges of the foot was documented. Generally, morphogenesis in the macaque was accelerated relative to that in the human fetus by approximately 3 weeks.