"The distal end sheath 111 is removably connected to the distal end of the intermediate sheath 110. [0351] The proximal end sheath 109 is formed of a plastic material which is comparatively flexible, the plastic material having excellent transparency such as polyurethane, vinyl chloride, polyurethane based elastomer, polystyrene based elastomer, or polyolefin based elastomer, for" . . . .