146 THE ABDOMEN. 



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 func- 

 tion 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 con- 

 nected 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 con- 

 stricting 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. 



