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Placenta is the intimate connection between the fetus and uterine wall of the mother to exchange the materials. The outer surface of the chorion in humans develops a number of finger like projections, known as chorionic villi, which grow into the tissue of the uterus. These villi, penetrate the tissues of the uterine wall in which they are embedded, make up the organ known as the placenta by means of which the developing embryo obtains nutrients and oxygen and gets rid of carbon dioxide and metabolic wastes. Because the chorion takes part in the formation of placenta, the human placenta is called the chorionic placenta. It consists of fetal part, the chorion and a maternal part the decidua basalis.