an apparatus for the operation of a working element of an excavator . an arm connected to the working element and a boom for supporting and operating the arm are fabricated each in the shape of a hollow tube whose opposite ends are left unclosed . a boom cylinder , an arm cylinder , or a working element cylinder is disposed as contained within the boom or the arm . the point of connection of the boom to the arm and the point of connection of the working element cylinder to the arm constitute a joint fulcrum . the point of connection of the boom cylinder to the boom and the point of connection of the arm cylinder to the boom similarly constitute a joint fulcrum .