ABSTRACT
The developing process of the hair of the fetal skin was studied. The ages of 103 human embryos and fetuses ranged from 4 to 40 gestation weeks. Ten different sites were selected, i.e., scalp, forehead, cheek, chest, abdomen, back, palm, sole, finger and toe. For the embryos 3 sites were studied, i.e., cephalic, trunk, and caudal portions. Following results were made: 1) The primitive hair germ was first noted the 10th week in the face skin as nubbins of mesenchymal cells beneath discrete foci of crowdes, elongated germinative epithelial cells. The developing hair germs and hair pegs were observes at the cephalic portion by 11 weeks. At 15 weeks the hair pegs including hair germs were noted in the trunk skin. The bulbous hair peg stage started at the 16th week in the cephalic portion and at the 18th week in the trunk. 2) Relative number of fetal hairs progressively increase up to 20 weeks of gestation but, thereafter decreased although it was different by the site of the body. 3) The diameter of fetal hair follicles increased with fetal age to the term with slight difference by the portion of body. 4) The developmental process of hair was more rapid in the cephalic portion than the trunk in views of morphologic changes of the hair structures, number and diameter of hair follicles.