In rabbit the opening of coronary sinus into the left precaval vein is found by a fold called :

Question

$\begin {array} {1 1} (1)\;Valve\: of\: Thebesius & \quad (2)\;Mitral\: Valve \\ (3)\;Tricuspid\: Valve & \quad (4)\;Valve\: of\: Eustachian \end {array}$