A surgical instrument for use with a surgical portal apparatus includes an elongate shaft defining a longitudinal axis. A dilating member disposed at a distal end of the elongate shaft and has a first longitudinal arc segment and a second longitudinal arc segment being in diametrical opposed relation. The first and second longitudinal arc segments define respective first and second radii of curvature transverse to the longitudinal axis, and decrease from proximal to distal to define a generally tapered configuration of the dilating member. The first radius of curvature is greater than the second radius of curvature at predefined longitudinal positions of the dilating member such that the first longitudinal arc segment extends distally beyond the second longitudinal segment to define a penetrating tip. The penetrating tip has a reduced profile and is dimensioned to facilitate initial insertion of the dilating member into tissue.
