Fig. 6. Three-dimensional models (A-C) and labeled diagrams (A'-C') showing atrial malformations of Cited2-null embryo hearts at 14.5 dpc. The models show the dorsal side of the atria (orange) and associated blood vessels (blue). (A,A') Normal, asymmetric atrial appendages. (B,B') Cited2-null hearts show symmetrical atrial appendages, each resembling a normal right atrium. The left superior vena cava (LSC) of the Cited2-null heart does not undercross the common space formed by pulmonary veins (PV): the symmetric arrangement of the pulmonary veins and the additional blood vessel (asterisk) to the right of the inferior vena cava (IVC). (C,C') Dorsal atrial wall from the ventral aspect of a Cited2-null heart, after removal of the ventricles and atrioventricular junction from the model. Between the left and right atrial appendages, there is a median chamber (MC, purple) that is incompletely separated from them by ridges protruding from the dorsal side (arrowheads), this MC receives all veins. RA, right atrial appendage; LA, left atrial appendage; RSC, right superior vena cava; O, orifice of the lung vein.