s called the jejunum, because it
is usually empty after death.

The remaining portion is named the ileum, because of the many folds
into which it is thrown. It is the longest part of the small intestine,
and terminates in the right iliac region, opening into the large
intestine. This opening is guarded by the folds of the membrane forming
the ileo-caecal valve, which permits the passage of material from the
small to the large intestine, but prevents its backward movement.

144. The Coats of the Small Intestine. Like the stomach, the small
intestine has four coats, the serous, muscular, sub-mucous,
and mucous. The serous is the peritoneum.[22] The muscular consists
of an outer layer of longitudinal, and an inner layer of circular fibers,
by contraction of which the food is forced along the bowel. The sub-mucous
coat is made up of a loose layer of tissue in which the blood-vessels and
nerves are distributed. The inner, or mucous, surface has a fine, velvety
feeling, due to a countless number of tiny, thread-like projections,
called villi. They stand up somewhat like the "pile" of velvet. It is
through these villi that the digested food passes into the blood.

[Illustration: Fig. 56.--Sectional View of Intestinal Villi. (Black dots
represent the glandular openings.)]

The inner coat of a large part of the small intestine is thrown into
numerous transverse folds called _valvulae conniventes_. These seem to
serve two purposes, to increase the extent of the surface of the bowels
and to delay mechanically the progress of the intestinal contents. Buried
in the mucous layer throughout the length, both of the small and large
intestines, are other glands which secrete intestinal fluids. Thus, in the
lower part of the ileum there are numerous glands in oval patches known as
_Peyer's patches_. These are very prone to become inflamed and to ulcerate
during the course of typhoid fever.

145. The Large Intestine. The large intestine begins in the
right iliac region and is about five or six feet long. It is much larger
than the small intestine, joining it obliquely at short distance from its
end. A blind pouch, or dilated pocket is thus formed at the place of
junction, called the caecum. A valvular arrangement called the
ileo-caecal valve, which is provided with a button-hole slit, forms a kind
of movable partition between this part of the large intestine and the
small intestine.

[Illustration: Fig. 57.--Tubular Glands of the Sma