Surgical preparation and exposure of fetal tissues for IVM. (A) An anesthetized pregnant mouse is placed on a plexiglass stage, the right uterine horn (1) exteriorized after lateral incision (2) and opened to expose one fetus (3) contained within its intact yolk sac and connected to the placenta (4). The fetus is then placed in a vacuum grease–containing Petri dish (5) and superfused with superfusion buffer. Fetal eye (6). (B) To visualize yolk sac microvessels, a coverslip (not shown) is placed over the exposed yolk sac. (C) A whole mount preparation of a wildtype YS (E14), fixed and stained with modified Giemsa reagent, shows the extensive network of developing blood vessels that are accessible for IVM and the villous nature of the tissue. The arrow points out one of the larger vitelline vessels.