Chuzhoi mutants exhibit reduced cervical flexure and abnormal heart looping. (A, B) Lateral views of E18.5 fetuses demonstrate reduced cervical flexure in chuzhoi mutants (B) compared to wild-type littermates (A). Lines are drawn between the mouth opening and centre of the ear, and parallel to the long axis of the spine. (C-F) Lateral (C, D) and ventral (E, F) views of wild-type (C, E) and chuzhoi mutant (D, F) E10.5 embryos show abnormal looping of the heart in the mutant embryo. Lines are drawn between the first branchial arches, along the base of the heart, and between the forelimb buds, indicating the abnormal flexure of the mutant embryo; the abnormal positioning of the heart appears to reflect the abnormal skewing of the embryo, likely owing to incomplete embryonic turning. The posterior region of the E10.5 embryos (caudal to the forelimb bud) have been removed to aid photography of the heart region.