The Urinary Tract

The urinary bladder (A) was incised and opened here to expose the entrance of the ureters (B) into the urinary bladder. The probes were placed in the orifices to show how the ureter penetrates the wall at an angle. What is the purpose of that?

The ureters enter the urinary bladder close to the beginning of the urethra (C). The triangle formed by the openings of the ureters and the beginning of the urethra is referred to as the trigone of the bladder (FYI).