Expansion
Truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium and sinus venosus
Expansion
| Embryonic segment | Adult derivative |
|---|---|
| Truncus arteriosus | Ascending aorta and pulmonary trunk |
| Bulbus cordis | Smooth outflow parts of both ventricles |
| Primitive ventricle | Trabeculated parts of both ventricles |
| Primitive atrium | Trabeculated (pectinate) parts of both atria |
| Sinus venosus | Smooth part of the right atrium, coronary sinus, part of the left atrium |
The smooth versus rough distinction inside each chamber is a direct fossil record of this development: the pectinate anterior right atrium is primitive atrium, the smooth posterior sinus venarum is sinus venosus, and the crista terminalis marks the join.
Failure of the truncus to divide gives persistent truncus arteriosus; unequal division gives tetralogy of Fallot.