During TURP, surgeon takes care to dissect above the verumontanum to prevent injury to:

Verumontanum is midline elevation on the posterior wall of the prostatic urethra. It acts as a surgical landmark. It lies immediately proximal to the external urethral sphincter. It thus serves as a distal landmark for prostatic resection in TURP to prevent injury to the external urethral sphincter. "The verumontanum serves as a significant landmark to stop resection because the external urethral sphincter lies just distal to it." - Reoperative Pelvic Surgery By Richard P. Billingham p225