Zonary placenta

Zonary placenta

The zonary deciduate placenta is present in the carnivores, and as the name indicates the chorionic villi are present in two transverse rows or zones over the surface of elongated blastocyst. The surfacial uterine mucosa (endometrium) becomes eroded along the ridges of two zones of villi. The villi are in close contact with the maternal tissues. They are highly branched in the uterine tissues. Each villous includes the allantois which grows upto the zonary extensions of blastocyst. The uterine wall with its branched villi is also known as decidua. The nutritive materials which are absorbed from the maternal blood in decidua is conducted to the embryo through the allantoic circulation. The contact between foetal tissues and maternal tissues is so intimate that at the time of birth much of superficial layer of uterine wall is lost with the placenta.