septum spurium septum spurium during development of the heart, the orifice of the sinus venosus lies obliquely, and is guarded by two valves, the right and left venous valves; above the opening these unite with each other and are continuous with a fold named the septum spurium. septum spuriuminterior of dorsal half of heart from a human embryo of about thirty days. (septum spurium labeled at upper left.)interior of dorsal half of heart of human embryo of about thirty-five days. (septum spurium labeled at upper left.)anatomical terminology