A surgical instrument for use with a surgical portal apparatus composing: an elongate shaft having proximal and distal ends (102,104) and defining a longitudinal axis; and a dilating member disposed at the distal end of the elongate shaft, the dilating member having a first longitudinal arc segment and a second longitudinal arc segment in diametrical opposed relation to the first longitudinal arc segment, the first and second longitudinal arc segments defining respective first and second radii of curvature (r1,r2) transverse to the longitudinal axis, the first and second radii of curvature decreasing from proximal to distal to define a generally tapered configuration of the dilating member, the first radius of curvature being 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 having a reduced profile and dimensioned to facilitate initial insertion of the dilating member into tissue, the shaft and dilating member being monolithically formed or bering formed by separate components joined to each other during manufacturing by the use of adhesives or welding, the instrument being characterized in that the elongate shaft defines a radius of curvature greater than the maximum value of the second radius of curvature of the second longitudinal arc segment wherein the juncture of the elongate shaft and the second radius of curvature defines a surface in general transverse relation to the longitudinal axis, the transverse surface extending about the second longitudinal arc segment. an elongate shaft having proximal and distal ends (102,104) and defining a longitudinal axis; and a dilating member disposed at the distal end of the elongate shaft, the dilating member having a first longitudinal arc segment and a second longitudinal arc segment in diametrical opposed relation to the first longitudinal arc segment, the first and second longitudinal arc segments defining respective first and second radii of curvature (r1,r2) transverse to the longitudinal axis, the first and second radii of curvature decreasing from proximal to distal to define a generally tapered configuration of the dilating member, the first radius of curvature being 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 having a reduced profile and dimensioned to facilitate initial insertion of the dilating member into tissue, the shaft and dilating member being monolithically formed or bering formed by separate components joined to each other during manufacturing by the use of adhesives or welding, the instrument being characterized in that the elongate shaft defines a radius of curvature greater than the maximum value of the second radius of curvature of the second longitudinal arc segment wherein the juncture of the elongate shaft and the second radius of curvature defines a surface in general transverse relation to the longitudinal axis, the transverse surface extending about the second longitudinal arc segment.