Formation of Separate Ureteric Openings and the Trigone
First, we show where the mesonephric ducts join with the developing bladder in approximately week 5; the ureteric buds are outgrowths of the mesonephric ducts.
The ends of the mesonephric ducts move inferiorly and incorporate into the bladder wall; notice that this also brings the ureteric buds in closer contact with the bladder.
As the mesonephric ducts continue their downward migration, the ureteric buds establish direct connections with the urinary bladder and cease to connect with the mesonephric ducts.
In the mature arrangement, the incorporated caudal portions of the mesonephric ducts contribute to formation of the trigone, which is a triangular region of the bladder bound superiorly by the two ureteric openings and the internal urethral opening inferiorly.
Be aware that the trigone is classically associated with incorporated mesonephric duct tissue; over time, its surface lining changes to endodermal epithelium.
Mature Urinary System Anatomy:
