_small_ and _large_. The _small intestine_ is a little over seventy feet in
length and about one and one-half inches in diameter. The mucous membrane
lining presents a large absorbing surface and is well supplied with
absorbing vessels that take up the sugars, proteids and fats, which are
finally distributed to the body cells by the blood capillaries. In addition
to these absorbing vessels the mucous membrane contains intestinal glands
that secrete the intestinal juice. Other digestive secretions from the
pancreatic gland and the liver are poured into the small intestine near its
origin. These digestive juices act on the proteids, sugars, starches and
fats, changing them into substances that are capable of being absorbed.

[Illustration: FIG. 14.--Photograph of model of digestive tract of horse:
oesophagus; stomach; liver; small intestine; large intestine; spleen.]

After disengaging itself from the mass of loops lodged in the region of the
left flank, the small intestine crosses to the region of the right flank,
where it terminates in the first division of the large intestine.

_The large intestine_ is formed by the following divisions: caecum, double
colon, floating colon and rectum. The caecum is a large blind pouch that
has a capacity of about seven gallons. The double colon is the largest
division of the intestines. It is about twelve feet in length and has a
capacity of about eighteen gallons. This portion of the intestine
terminates in the region of the left flank in the floating colon. The
latter is about ten feet in length and about twice the diameter of the
small intestine, from which it can readily be distinguished by its
sacculated walls. The rectum is the terminal portion of the intestinal
tract. It is about one and one-half feet in length and possesses heavy,
elastic walls.