what does the primitive heart form
The two tubes migrate together and fuse to form a single primitive heart tube, the tubular heart which quickly forms five distinct regions. From head to tail, these are the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus.he heart is the first functional organ in vertebrate embryos, and in the human, beats spontaneously by week 4 of development.