Fig. 6. The structure of the trigone is likely to depend on intercalation of ureteral and bladder muscle. (A) A sagittal section through an E17 Pax2^+/+ embryo showing the point at which the ureteral longitudinal fibers join the bladder detrusor (yellow arrows). (B) A sagittal section through a Pax2^-/- littermate of that shown in A, showing the structure of the trigone region in the absence of the ureter. Note the abundant bladder and urethral muscle, and the tunnel through the bladder (red arrow) present in both wild type (A) and mutant (B). det, detrusor. Magnification: x100.