A cannula (10) receives surgical instruments (120) for performing a surgical procedure on a body (130). The cannula (10) comprises a tube structure (12) defining a passage (16) through which the surgical instruments (120) are inserted into the body (130). The tube structure (12) has a proximal end (20) and a distal end (62). The tube structure (12) includes an expandable portion (40) for enabling an increase in the cross-sectional area of the passage (16) at the distal end (62). The expandable portion (40) of the tube structure (12), when expanded, has a conical configuration.