Greater omentum

The greater omentum (great omentum; gastrocolic omentum; epiploon) is a large fold of peritoneum that hangs down from the stomach, and extends from the stomach to the posterior abdominal wall after associating with the transverse colon.

Structure
The greater omentum is the largest peritoneal fold. It consists of a double sheet of peritoneum, folded on itself so that it is made up of four layers.

The two layers which descend from the stomach and commencement of the duodenum pass in front of the small intestines, sometimes as low down as the pelvis; they then turn upon themselves, and ascend again as far as the transverse colon, where they separate and enclose that part of the intestine.

These individual layers may be easily demonstrated in the young subject, but in the adult they are more or less inseparably blended.

The left border of the greater omentum is continuous with the gastrolienal ligament; its right border extends as far as the commencement of the duodenum.

The greater omentum is usually thin, presents a cribriform appearance, and always contains some adipose tissue, which in obese people accumulates in considerable quantity.

Between its two anterior layers, a short distance from the greater curvature of the stomach, is the anastomosis between the right and left gastroepiploic vessels.

Subdivisions
The greater omentum is often defined to encompass a variety of structures, and can thus be subdivided into the following:
 * Gastrophrenic ligament
 * Gastrosplenic ligament
 * Phrenicosplenic ligament
 * Splenorenal ligament
 * Pancreaticosplenic ligament
 * Pancreaticocolic ligament
 * Splenocolic ligament
 * Phrenicocolic ligament

Development
The greater omentum develops from the dorsal mesentery that connects the stomach to the posterior abdominal wall. During stomach development, the stomach undergoes its first 90° rotation along the axis of the embryo, so that posterior structures are moved to the left and structures anterior to the stomach are shifted to the right. As a result, the dorsal mesentery folds over on itself, forming a pouch with its blind end on the left side of the embryo. A second approximately 90° rotation of the stomach, this time in the frontal plane, moves structures inferior if they were originally to the left of the stomach, and superior if they were originally to the stomach's right. Consequently, the blind-ended sac (also called the lesser sac) formed by the dorsal mesentery is brought inferiorly, where it assumes its final position as the greater omentum. It grows to the point that it covers the majority of the small and large intestine.