A cannula, comprising a tube (5), with a head (2) at its distal end consisting of a cone-shaped rigid ring (3) and connected to it on the other side of a flexible ring (4). On the whole length of the head (2) and on a part of the tube (5) near the connection to the head (2), from the inside, there is a thin guide sleeve (6) which, on the section of the rigid ring (3) is permanently attached to the surface of its wall, while on its remaining length, it is slidably movable relative to the wall of the tube (5). The guide sleeve (6) is equipped with at least two tie rods (9) attached, on one end, opposite to each other, to the wall of the guide sleeve (6).
