to the left, to the anus, the external opening. This opening is guarded by two sphincter muscles, about an inch apart, the internal and external sphincters. The coils of the small intestine lie below the transverse colon, covered mostly by the omentum. The splenic flexure is behind the stomach and below the spleen and is slightly higher than the hepatic flexure. The sigmoid flexure can be felt in the left inguinal region in thin people.
The fact that the rectum is somewhat to the left is of importance in childbirth because if the rectum is packed, it may turn the child's head in the wrong direction.
No digestion goes on in the large intestine, the function being to dry by absorbing water. The movements are practically the same as those of the small intestine except that they are much less active. Fermentation makes the contents acid. By the time food reaches the rectum it has been thoroughly digested and has given up its nourishment. It is then expelled as waste matter or feces. Defecation combines the involuntary movements of peristalsis and relaxation of the sphincters with the voluntary aid of the abdominal muscles. The ano-spinal reflex, by which movements of the bowel are regulated, is in the lumbar enlargement of the cord.
The hemorrhoidal veins in the lower rectum are connected with both the systemic and the portal veins and have no valves so that, as they are subjected to much strain, they often become varicose and dilated. This condition is called hemorrhoids or piles. Obstruction of the intestine may be caused by the growth of a constricting band, by intussusception or telescoping of the intestine on itself, especially at the ileocecal valve, or by volvulus or twisting. Foreign bodies are sometimes found in the appendix but they are not usually the cause of appendicitis. Cancer of the intestine is common and its mass is apt to cause obstruction with all its attendant symptoms. It may necessitate an artificial anus. Hernia or rupture may also occur and the hernia may become strangulated.
