The small intestine is that portion of the alimentary canal which begins at the stomach and ends at the large intestine. Its usual length is twenty feet. The diameter, which at the upper portion (duodenum) is two inches, gradually becomes less, until at the lower end it is but one inch. Now, the length of the inner coat of this small intestine--the mucous membrane--is about _double_ that of the intestine itself. Think of wearing a coat twice as long as yourself! How do you think this is accomplished in the case of the muscular tube under consideration? Well, Nature, having a most peculiar function to perform, has thrown this mucous coat or tube into a thousand folds (valvulæ conniventes, or “winking valves”). These folds form valves, occupying from one-third to one-half the circumference of the bowel. The greatest width of each fold is at the center, where it measures from a quarter to half an inch. Over this great expanse of mucous membrane we find studded ten million five hundred thousand intestinal villi, whose office it is to absorb the food substances in their passage through the canal. [Illustration: Fig. 9. Stomach, liver, small intestine, etc. (Flint.) 1, inferior surface of the liver; 2, round ligament of the liver; 3, gall-bladder; 4, superior surface of the right lobe of the liver; 5, diaphragm; 6, lower portion of the œsophagus; 7, stomach; 8, gastro-hepatic omentum; 9, spleen; 10, gastro-splenic omentum; 11, duodenum; 12, 12, small intestine; 13, cæcum; 14, appendix vermiformis; 15, 15, transverse colon; 16, sigmoid flexure of the colon; 17, urinary bladder.] Those that have observed the anatomical illustrations of the small intestines must have been struck by their apparently inextricably tangled convolutions. In life, these convolutions are constantly changing their locations, as though they were a mass of worms. The large intestine begins at the cæcum and extends to the anus, or vent of the intestinal sewer. It is called the colon--the ascending, transverse, and descending colon. It is about five feet in length. Its diameter is the greatest at the cæcum, where it measures, when moderately distended, two and a half to three and a half inches. Beyond the cæcum the diameter is one and two-thirds to two and two-thirds inches, the smallest part being at the upper end of the rectum. The muscular movements of the large intestine are much more limited in number and range than those of the small intestines. The area of its mucous membrane is also much less, notwithstanding the fact that it is thrown into sacculated pouches, or sacculi, by the contraction of the longitudinal muscular bands of the bowel. [Illustration: Fig. 10. The cæcum, dorso-mesial view, showing the ileum-side of the ileo-cæcal valve, and the beginning of the three muscular ribbons. (Gerrish.)]