The hinder part of the urethral bulb lies in apposition with the inferior fascia of the urogenital diaphragm, but its upper portion diverges somewhat from this fascia: the anterior wall of the membranous urethra is thus prolonged for a short distance in front of the urogenital diaphragm; it measures about 2 cm in length, while the posterior wall which is between the two fasciæ of the diaphragm is only 1.25 cm long.
The distal part of the urethral bulb lies against the inferior fascia of the urogenital diaphragm, but its upper portion deviates from this fascia; the anterior wall of the membranous urethra extends forward for a short distance in front of the diaphragm; it measures about 2 cm in length, while the posterior wall situated between the two diaphragmatic fascial layers is only 1.25 cm long.