The<unk>  (also called the spiral septum, or aortic septum in older texts) is developmentally formed from neural crest, specifically the cardiac
neural crest, and actively separates the aorta and pulmonary arteries and fuses with the interventricular septum within the heart during development. 
The actual mechanism of septation of the outflow tract is poorly understood, but is recognized as a dynamic process with contributions from contractile, hemodynamic, and extracellular matrix interactions.
Aorticopulmonary septum
Aortic arches
Tracheoesophageal septum
Aortopulmonary Window
Interatrial septum
Base of the heart
Interventricular septum
Transverse intermuscular septum