ULTRASTRUCTURE OF PLACENTA AND FETAL MEMBRANES OF DOG .I. PLACENTAL LABYRINTH

The ultrastucture of the canine placental labyrinth has been studied at 40 to 60 days of gestation. Cytotrophoblasts persist in an undifferentiated state throughout gestation, with numerous polyribosomes and little rough endoplasmic reticulum, with expanded cisterns containing flocculent precipitate. Fetal capillaries progressively invade the syncytium, without, however, penetrating the basal lamina. Maternal decidual cells are reported here for the first time in this species. The maternal endothelium is considerably hypertrophied, with many profiles of membranous organelles; but there is consideriable thinning of this endothelium between 50 and 60 days. The interstitial membrane intervenes between trophoblast and maternal endothelium, often forming the thickest part of te barrier at 60 days. the definitive endotheliochorial condition is confirmed; and the thinnest barrier is about 1 μ. Copyright © 1969 Wiley‐Liss, Inc.