Remove a piece that includes the fetal surface and intact maternal surface, about 3-4 cm from the cord insertion. If not, label them arbitrarily and make a statement to that effect. Attempt to determine grossly whether the dividing membrane has chorion or not, according to the accompanying tables. The latter can be better demonstrated by injecting the artery of one twin along the place of fusion of the placenta with 30-50 cc of saline solution containing a dye and noting whether the fluid emerges from the vein of the other twin through one or more common villous lobules. The placenta must be intact to perform this test.
Arteries always run over veins.
Examine each half as a singleton placenta.