may be found in the copending u s patent application ser no 10 661 159 u201c shape transferring cannula system and method of use u201d by the inventor of the present invention filed sep 12 2003 and is incorporated herein by reference the cannula 101 may include segments with independently controllable rigidity or may include a first segment 105 with a cross section that is different from a second segment 110 in particular embodiments the second segment 110 is adapted to accommodate a steerable tip 128 of the insertable device 125 wherein the displacement limited coupling maintains an overlap between the steerable tip 128 and the second segment 110 the displacement limited coupling may also act to prevent overlap between steerable tip 128 and the first segment 105 fig2 shows an exploded view of the cannula system shown in fig1 the displacement limiting coupling 115 has a portion 205 that mates to a surface 210 of the endoscope 125 thus capturing the endoscope 125 and maintaining it in a fixed position with respect to the displacement limiting coupling 115 the displacement limiting coupling 115 also captures the cannula 101 a first wall 215 and a second wall 220 define the limits for the axial travel of the cannula 101 a guide 225 extending from the second wall 220 may be used to support the cannula 101 the difference between the width of the actuator 120 and the distance between the first wall 215 and second wall 220 establishes the maximum allowable axial displacement between the cannula 101 and the endoscope 125 in one embodiment the range of allowable positions.