A method and device for processing a carcass-part of slaughtered poultry in a processing line is provided. Means are applied for cutting the membrana and/or removing of the wishbone from the carcass-part. The means for cutting the membrana and/or removing of the wishbone include an arrow-shaped knife and two blades arranged on opposite sides of the knife. After the means for cutting the membrana and/or removing of the wishbone are introduced into the carcass part, the arrow-shaped knife and the two blades are moved in a unitary movement from within the carcass-part in a sideways direction away from the carcass part so as to lift the wishbone legs while they are still connected to the wing joints, and subsequently turn the wishbone legs out of the wing joints of the carcass-part.