A surgical instrument comprising: a mount body (22, 122) having a top portion, a distal end, a proximal end and a bottom portion; an arm (12, 112) extending distally from a joint member (30, 130) of the mount body, wherein the arm (12, 112) comprises a plurality of articulating links (40,140) that allow the arm to be flexible in a first configuration and which can be compressed to render the arm substantially rigid in a second configuration; a working end (14, 114) for contacting tissue, the working end mounted to a distal end of the arm; an actuator (52, 52'); and a cable extending from the actuator (52, 52') through the mount body, the joint member, and the arm, wherein the actuator (52, 52') is mounted to the mount body towards the proximal end of the mount body; wherein the actuator (52, 52') and the cable are configured to change a state of the arm between the first flexible and the second rigid configurations by rotation of the actuator (52, 52') in a first direction and from the second rigid configuration to the first flexible configuration by rotation of the actuator counter to the first direction, wherein rotation of the actuator (52, 52') in the first rotational direction increases tension in the cable, thereby fixing the orientation of the arm with respect to the mount body in the rigid configuration; and wherein the joint member (30, 130) is pivotally mounted at a distal end portion of the mount body to allow positioning of a proximal portion of the arm (12, 112), wherein the joint member comprises: a first joint member (34, 134) configured to constrain movement to yawing; and characterized in that the joint member further comprises a second joint member (36,136) configured to constrain movement to pitching. a mount body (22, 122) having a top portion, a distal end, a proximal end and a bottom portion; an arm (12, 112) extending distally from a joint member (30, 130) of the mount body, wherein the arm (12, 112) comprises a plurality of articulating links (40,140) that allow the arm to be flexible in a first configuration and which can be compressed to render the arm substantially rigid in a second configuration; a working end (14, 114) for contacting tissue, the working end mounted to a distal end of the arm; an actuator (52, 52'); and a cable extending from the actuator (52, 52') through the mount body, the joint member, and the arm, wherein the actuator (52, 52') is mounted to the mount body towards the proximal end of the mount body; wherein the actuator (52, 52') and the cable are configured to change a state of the arm between the first flexible and the second rigid configurations by rotation of the actuator (52, 52') in a first direction and from the second rigid configuration to the first flexible configuration by rotation of the actuator counter to the first direction, wherein rotation of the actuator (52, 52') in the first rotational direction increases tension in the cable, thereby fixing the orientation of the arm with respect to the mount body in the rigid configuration; and wherein the joint member (30, 130) is pivotally mounted at a distal end portion of the mount body to allow positioning of a proximal portion of the arm (12, 112), wherein the joint member comprises: a first joint member (34, 134) configured to constrain movement to yawing; and characterized in that the joint member further comprises a second joint member (36,136) configured to constrain movement to pitching. a first joint member (34, 134) configured to constrain movement to yawing; and characterized in that the joint member further comprises a second joint member (36,136) configured to constrain movement to pitching.