The sigmoid vein is also called the vena sigmoideus and refers to one group of sigmoid veins that are tributaries of the inferior mesenteric vein, which is a tributary to the hepatic portal vein. Each sigmoid vein is curved or crescent-shaped like the uncial sigma, which resembles the letter c. These veins travel through the colon's curved part into the rectum. The function of each sigmoid vein is to drain the sigmoid colon, the portion of the large intestine closest to the anus and rectum. The sigmoid colon, part of the digestive system, must be drained in order to properly extract salt and water from solid wastes before the body eliminates them. The inferior mesenteric vein receives each sigmoid vein from the iliac and sigmoid colons. The sigmoid vein empties into the superior rectal vein, which later turns into the inferior mesenteric vein. The sigmoid vein is one part of the body's blood vessel system, the main purpose of which is to carry blood to the heart.