Which statement best describes the inferior mesenteric aery

The left colic aery is a branch of inferior mesenteric aery. It has ascending and descending branches. In a sigmoid colectomy the ascending branch is preserved to maintain the blood supply of the proximal descending colon. The inferior mesenteric aery arises from the aoa at the level of the subcostal plane, 3-4 cm above the aoic bifurcation. This is at the level of L3 and approximately at the level of the umbilicus. The inferior mesenteric aery supplies the mucous membrane as far as the dentate line, which is found in the anus. This line represents a watershed between the superior rectal branch of the inferior mesenteric aery, and the middle and inferior rectal aeries which are derived from the internal iliac aery. The inferior mesenteric aery enters the pelvis by crossing the pelvic brim at the level of bifurcation of the left common iliac aery.