Phenotype of Thbd^−/− embryos in Thbd^+/− mothers. Thbd-expressing embryos (A,C,E,G) are shown with their respective Thbd^−/− littermates (B,D,F,H). Embryos in panels A through D and E through H were photographed at E9.5 and E10.5, respectively. Thbd^−/− embryos are resorbed by E9.5 (B). In mothers lacking the thrombin receptor Par4 (C,D), and in mothers lacking platelets due to Nfe2 deficiency (E,F) or anti-GP1bα antibody–induced depletion (G,H), Thbd^−/− embryos completed axonal rotation (“turning”), a hallmark of transition from E8.5 to E9.5 stage of development. Embryos were photographed in water using equipment described in “Histology.” Scale bars represent 1 mm.