Skulls of Wnt1-Cre; Msx1cko/cko; Msx2cko/cko mutants at the newborn stage were stained with Alizarin Red to reveal bone. A, wild type; B, Msx1cko/+;Msx2cko/+; C, Msx1cko/+;Msx2cko/cko; D, Msx1cko/cko; Msx2cko/+; E, Msx1cko/cko; Msx2cko/cko. At least five skulls of each genotype were examined. We show representative images. Note increasing size of frontal foramen with decreasing Msx gene dosage up to homozygote-heterozytgote combination (arrows). Note unpatterned, heterotopic bone in area of posterior frontal bone in E (bracket). Images are representative of at least four skulls with similar morphology.