The extensive fold of peritoneum by which
the jejunum and ileum
are attached to and suspended from the posterior wall of the abdomen.
Anteriorly, the mesentery has a free border where its two layers are continuous
with each other and enclose the jejunum and ileum. This border is necessarily
as long as the intestine which it encloses – i.e., about 20 feet –
but this great length is not apparent because the mesentery is thrown into
undulating folds to accommodate itself to the coils of the intestine. The
parietal border is called the root of the mesentery, and
is only about 15 cm (6 in.) in length. The depth of the mesentery from root
to intestine, over a great part of its extent, is 15–20 cm (6–8
in), and diminishes to nothing at each end.
|The mesentery in a subject which was hardened by
formalin injection. The jejunum and ileum have been removed, and the
foldings of the mesentery are displayed.
of the mesentery
The root extends obliquely from the duodenal-jejunal flexure to the entrance
of the ileum into the large intestine,
and crosses in sequence (1) the duodenum,
(2) the aorta, (3) the inferior
vena cava, and (4) the right psoas major with the ureter and testicular
(or ovarian) vessels on its surfaces.
Contents of the
The contents of the mesentery, in addition to the intestine (though that
is a matter of definition), are: (1) Extraperitoneal tissue and a variable
quantity of fat. (2) Over a hundred mesenteric lymph glands – largest
and most numerous near the root with large numbers of "lacteal" lymph vessels
passing to them from the intestine. (3) Superior mesenteric vessels in the
root, and their numerous branches and tributaries which supply the jejunum
and ileum. (4) A very large number of soft sympathetic nerves for the supply
of the intestine. This generous supply entails the cutting of a large number
of nerves when a portion os the intestine is removed and section of the
nerves accounts for the "surgical shock" that follows such an operation.