FIG. 14A is a plan view of another embodiment of the ridges 76 depicted in FIG. 8C. FIG. 14B is an enlarged cross-sectional view of another embodiment of the ridges 76 depicted in FIG. 8D. FIGS. 14A and 14B depict two ridges 76C on the inner surface 158C of the sheath body 40C that form at least one channel 156C between the sheath body 40C and the dilator shaft 36C.