A surgical instrument for joining tissue surgically, the surgical instrument comprises: a handle assembly (160)； an elongated part (120) extending distally from the handle assembly and defining a longitudinal axis； an end effector disposed adjacent to a distal portion of the elongated part, the end effector includes a first member (330) of the jaw and a second member (340) of the jaw, at least one of the first member of the jaw and the second jaw member is movable relative to the other jaw member between the separated and approximate positions, the first jaw member includes an upper surface (332) of contact with the tissue and a lower part (334) of the tray, the part of the tray includes a groove (336) defined therein； an immobilizer member (370) disposed adjacent to a distal part of the first jaw member, the immobilizer member is pivotable with respect to the first jaw member between a first position where a significant part of the immobilizer member is located outside the first member of the jaw, and a second position where the immobilizer member fits inside the first member (330) of the jaw so that it does not protrude above the upper surface of contact with the tissue or below the bottom of the tray, characterized whereby the immobilizer member includes a lip (372) that extends downward from a lower surface of the immobilizer member that defines an immobilizer part (374), and wherein the lip (372) is located within the groove (336) of the part of the tray when it is in the second position.Un instrumento quirúrgico para unir tejido quirúrgicamente, el instrumento quirúrgico comprende: un conjunto (160) del mango； una parte alargada (120) que se extiende distalmente desde el conjunto del mango y que define un eje longitudinal； un efector extremo dispuesto contiguo a una parte distal de la parte alargada, el efector extremo incluye un primer miembro (330) de la mandíbula y un segundo miembro (340) de la mandíbula, al menos uno del primer miembro de la mandíbula y d
