human race. The caecum gradually blends into the second division of the
large intestine, called the colon.

_The colon_ consists of four parts, described as the ascending colon, the
transverse colon, the descending colon, and the sigmoid flexure, or
sigmoid colon. The first three divisions are named from the direction of
the movement of materials through them and the last from its shape, which
is similar to that of the Greek letter sigma ({~GREEK CAPITAL LETTER SIGMA~}).

_The rectum_ is the last division of the large intestine It is a nearly
straight tube, from six to eight inches in length, and connects with the
external surface of the body.

The general structure of the large intestine is similar to that of the
small intestine, and, like the small intestine, it is held in place by the
peritoneum. It differs from the small intestine, however, in its lining of
mucous membrane and in the arrangement of the muscular coat. The mucous
membrane presents a smooth appearance and has no villi, while the
longitudinal layer of the muscular coat is limited to three narrow bands
that extend along the greater length of the tube (Fig. 74). These bands
are shorter than the coats, and draw the large intestine into a number of
shallow pouches, by which it is readily distinguished from the small
intestine (Fig. 71).

[Fig. 74]

Fig. 74--*Section of large intestine*, showing the coats. 1. Serous coat.
2. Circular layer of muscle. 3. Submucous coat. 4. Mucous membrane. 5.
Muscular bands extending lengthwise over the intestine.

*Work of the Large Intestine.*--The large intestine serves as a receptacle
for the materials from the small intestine. The digestive fluids from the
small intestine continue their action here, and the dissolved materials
also continue to be absorbed. In these respects the work of the large
intestine is similar to that of the small intestine. It does, however, a
work peculiar to itself in that it collects and retains undigested food
particles, together with other wastes, and ejects them periodically from
the canal.

*Work of the Alimentary Muscles.*--The mechanical part of digestion is
performed by the muscles that encircle the food canal. Their uses, which
have already been mentioned in connection with the different organs of
digestion, may be here summarized: They supply the necessary force for
masticating the food. They propel the food through the canal. They