The narrowest pa of ureter is:

The constrictions of th ureter are three in number as follows : (i) At the junction of pelvis of the ureter with abdominal pa of the ureter. (ii) At the pelvic brim. (iii) Where it pierces the bladder. It is narrowest here Ureter: The ureter is a retroperitoneal, distensible muscular tube that connects the kidney with the bladder. It runs downward and medialward in front of the Psoas major and, entering the pelvic cavity, finally opens into the fundus of the bladder. The slit like lumen of the ureter has a stellate appearance because its mucosa is folded longitudinally. Aeries and veins: The aeries supplying the ureter are branches from the renal, internal spermatic, hypogastric, and inferior vesical. Nerves: The nerves are derived from the inferior mesenteric, spermatic, and pelvic plexuses. Constrictions - There are three normal anatomical constrictions where a stone from the renal pelvis can become lodged. The sites are;1) The ureteropelvic junction2) Site where it crosses the iliac vessels3) Ureterovesicular junction: Passage of ureter through the bladder wall Ref: Thieme Atlas of Anatomy: Neck and Internal Organs, edited by Lawrence M. Ross, Edward D. Lampei, Page 232