In cadavers, this opening is 2-3 mm in diameter, but in uterine tubes removed during operation it is found to be physiologically closed. The opposite opening of the tube, through which it opens into the cavity of the  uterus, is called the uterine opening (ostium uterinum tubae).      Structure of the wall of the tube. Immediately under the peritoneum, or serous coat (tunica serosa) is a connective-tissue coat (tunica subserosa) containing vessels and nerves. Medical coding training india will train you all these for the coding and billing and also for the payment and collections for the services performed in the office.