Formation of placenta :
(i) After implantation, finger-like projections appear on the trophoblast called chorionic villi.
(ii) Chorionic villi are surrounded by the uterine tissue and maternal blood.
(iii) The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal blood called placenta.
