The Large Intestine (Fig. 49), forming the final portion of the alimentary canal, is about 5 feet (1.5 meters) long, and varies in diameter from 2 1/2 to 1 1/2 inches (6-4 centimeters). Anatomists describe it as consisting of the cæcum (cc) with its vermiform appendix, the colon (ac, tc, dc), and the rectum (r). The small intestine does not open into the end of the large but into its side, some distance from its closed upper end; the cæcum is that part of the large intestine which extends beyond the communication. From it projects the vermiform appendix, a narrow tube not thicker than a cedar pencil, and about 4 inches (10 centimeters) long. The colon commences on the right side of the abdominal cavity where the small intestine communicates with the large, runs up for some way on that side (ascending colon), then crosses the middle line (transverse colon) below the stomach, and turns down (descending colon) on the left side, and there makes an S-shaped bend known as the sigmoid flexure; from this the rectum proceeds to the opening by which the intestine communicates with the exterior. The mucous coat of the large intestine possesses no villi nor valvulœ conniventes; it contains numerous closely set glands much like the crypts of Lieberkühn of the small intestine.

Diagram of abdominal part of alimentary canal.

Where do we find the crypts of Lieberkühn? Describe them. Where are the glands of Brunner?

Give the dimensions of the large intestine. Of what parts is it made up? How does the small intestine open into it? What is the cæcum? The vermiform appendix? Its size?

The Ileo Colic Valve

Where the small intestine joins the large there is a valve formed by two flaps of the mucous membrane sloping down into the colon, and so arranged as to allow matters to pass readily from the ileum into the large intestine, but not the other way.