Which of the following statements is true of cardiac development?

The heart forms during the third week by the apposition of left and right endocardial tubes as the head fold progresses caudally The endocardial tubes fuse to form a single-tube heart. This fusion begins cranially in the region of the bulbus cordis (outflow trunks) and proceeds caudally through the ventricles and the atria to the sinus venosus, which is incorporated into the atrium after loop formation. Rapid proliferation of the ventricular region results in the single-tube heart bending into an S-shaped loop. During this process, the dorsal mesocardium partially breaks down, which leaves the heart suspended only at the cranial and caudal ends; the discontinuity in the mesocardium is the transverse sinus. The left and right sides of the heart are established by the subsequent division of the single tube heart, not by the apposition of left and right endocardial tubes.