The<unk>  (Thebesian valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of the<unk><unk> .
It is named for Adam Christian Thebesius.
The valve may vary in size, or be completely absent.
It may prevent the regurgitation of blood into the<unk>  during the contraction of the atrium.
This valve may be double or it may be cribriform.
Valve of the coronary sinus
Atrioventricular nodal branch
Interventricular septum
Tricuspid valve
Interatrial septum
Atrioventricular node
Atrioventricular canal
Pulmonary valve