Sigmoid colon

The sigmoid colon (pelvic colon) is the part of the large intestine that is closest to the rectum and anus. 

It is completely surrounded by peritoneum (and thus is not retroperitoneal), which forms a mesentery (sigmoid mesocolon), which diminishes in length from the center toward the ends of the loop, where it disappears, so that the loop is fixed at its junctions with the iliac colon and rectum, but enjoys a considerable range of movement in its central portion.

Pelvic splanchnic nerves are the primary source for parasympathetic innervation. Lumbar splanchnic nerves provide sympathetic innervation via the inferior mesenteric ganglion.