Abstract: This invention relates to an instrument for extracting foreign bodies from physiological canals or ducts in the human body, the instrument comprising a catheter containing an inner cable terminating in a slide on which is mounted an outer basket which moves the walls of the physiological canal apart and this outer basket contains therewithin a basket for extracting the foreign body; the spacer basket thus maintains the walls of the physiological canal away from any rough edges of the body to be extracted, thus preventing the edges from injuring the walls. The invention is more particularly applicable to a catheter for extracting calculi from physiological canals or ducts.