Over-tube, method of manufacturing over-tube, method of disposing over-tube, and method of treatment in abdominal cavity

A method of disposing an over-tube including an inner cavity and an internal cover disposed in the inner cavity thereof, each of the inner cavity and the internal cover being able to alternatively insert an endoscope and a treatment device, the method, comprising:

• inserting the endoscope into the internal cover;
• inserting the over-tube into a body cavity from a natural opening in a patient's body in a state that the endoscope is inserted into the internal cover;
• arranging a distal end portion of the over-tube within a lumen wall of the body cavity;
• removing the endoscope and the internal cover from the inner cavity of the over-tube to a proximal side of the over-tube;
• and
• inserting the treatment device into the inner cavity of the over-tube,
• wherein:
• a tip end of the internal cover is engaged with an outer peripheral portion of the distal end portion of the over-tube, and
• the removing the internal cover from the inner cavity of the over-tube includes pulling off the internal cover to the proximal side of the over-tube after the over-tube is arranged within the lumen wall of the body cavity, releasing an engagement between the tip end of the internal cover and the outer peripheral portion of the over-tube, and extracting the internal cover from the inner cavity of the over-tube.