A surgical device (50) is adapted to facilitate access through an incision (100) in a body wall (18) having an inner surface and an outer surface, and into a body cavity of a patinet. The device includes (55) and second (65) retention members adapted to be disposed in proximity to the outer surface and the inner surface of the body wall, respectively. A membrane (75) extending between the two retention members form a throat (90) which is adapted to extend through the incision (100) and form a first funnel extending from the first retention member (55) into the throat (90), and a second funnel extending from the second retention member (65) into the throat (90). The throat of the membrane has characteristics for forming an instrument seal in the presence of an instrument and a zero seal in the absence of an instrument. The first retention member (55) may include a ring with either a fixed or variable diameter.