septum spurium

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sep·tum spu·'ri·um

a septum in the right atrium of the embryonic heart formed by the right venous valve and its continuation onto the dorsocephalic wall of the atrium; in human embryos, it reaches its fullest development during the third month and then undergoes regression, taking no part in atrial partitioning (hence its designation as false); reduced portions persist as the valve of the inferior vena cava and the valve of the coronary sinus.
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