ed on to the
stomach (St) forming the anterior layer of the _gastro-hepatic_ or
_lesser omentum_. It now covers the front of the stomach, and at the
lower border runs down as the anterior layer of an apron-like fold, the
_great omentum_, which in some cases reaches as low as the pubes; then
it turns up again as the posterior or fourth layer of the great omentum
until the transverse colon (C) is reached, the posterior surface of
which it covers and is reflected, as the posterior layer of the
_transverse meso-colon_, to the lower part of the pancreas (P); after
this it turns down and covers the anterior surface of the third part of
the duodenum (D) till the posterior wall of the abdomen is reached, from
which it is reflected on to the small intestine (I) as the anterior
layer of the _mesentery_, a fold varying from 5 to 8 in. between its
attachments. After surrounding the small intestine it becomes the
posterior layer of the mesentery and so again reaches the posterior
abdominal wall, down which it runs until the rectum (R) is reached. The
anterior surface of this tube is covered by peritoneum to a point about
3 in. from the anus, where it is reflected on to the uterus and vagina
(V) in the female and then on to the bladder (B); in the male, on the
other hand, the reflection is directly from the rectum to the bladder.
At the apex of the bladder, after covering the upper surface of that
organ, it is lifted off by the urachus and runs up the anterior
abdominal wall to the umbilicus, from which the start was made. All this
is the greater sac. The tracing of the lesser sac may be conveniently
started at the transverse fissure of the liver, whence the membrane runs
down to the stomach (St) as the posterior layer of the lesser omentum,
lines the posterior surface of the stomach, passes down as the second
layer of the great omentum and up again as the third layer, covers the
anterior surface of the transverse colon (C) and then reaches the
pancreas (P) as the anterior layer of the transverse mesocolon. After
this it covers the front of the pancreas and in the middle line of the
body runs up below the diaphragm to within an inch of the anterior layer
of the coronary ligament of the liver; here it is reflected on to the
top of the Spigelian lobe of the liver to form the posterior layer of
the coronary ligament, covers the whole Spigelian lobe, and so reaches
the transverse fissure, the starting-point.

[Illustration: FIG. 2.--Diag