Abstract
A morphological study on porcine placentae containing a fetus ranging from 1.5cm (ca. 25 days in pregnancy) to 32cm (near term) in C. R. length was undertaken. When a fetus attained 2.6cm in C. R. length (ca. 30 days), the chorionic epithelium showed a differentiation into ridge and fossa. Concomitant with this, fetal capillaries penetrating the epithelium were noted at the ridge and specific colloid droplets appeared in the epithelium of the chorionic fossa. Epithelial cells of the uterus gradually changed into cuboidal to squamous form with the progress of the gestation. No difference in character of the uterine epithelium between those facing the ridge and the fossa was noted. Light-microscopically, the surface of contact of the trophoblast with the uterine mucosa consisted of a fine interdigitation by both epithelia and it reacted strongly to PAS and alcian blue (pH2.5). Up to the stage when a fetus attains 3.5cm in C. R. length (ca. 35 days), nucleated erythrocytes were present exclusively in allantoic vessels. Nucleated erythrocytes were far less in number in allantoic vessels of placentae containing a fetus of 4.2cm and 4.9cm in C. R. length (ca. 40 days). Thereafter, only mature erythrocytes were present. The intraepithelial distribution of fetal capillaries secmed to persist until the term and as fetal capillaries reached the supranuclear region of the trophoblast of a definitive placenta of near term, the distance from the endothelium of the capillary to the apical margin of the epithelium measured less than 1.5μm. On the other hand, the capillaries in the chorionic fossa as well as in the endometrium did not invade the epithelium throughout the gestation period. Intracellular colloid droplets in a trophoblast of the fossa disappeared gradually in a late pregnancy (probably later than ca. 70 days). During pregnancy, uterine glands continued to increase in diameter and the secretions increased also in quantity. The development of the superficial gland was more remarkable than that of the deep gland being particularly appreciable during a middle stage of gestation (ca. from 40 days to 80 days).
