Two double-sided sheets of peritoneum, the greater omentum and the lesser omentum, extend from the greater curve and lesser curve of the stomach. We'll digress for a minute to look at them.
The greater omentum is attached along the whole length of the greater curve, the lesser omentum is attached along the lesser curve: up here its attachment is quite wide.
This is the lesser omentum. Parts of it are fatty, other parts are extremely thin. The lesser omentum goes from the lesser curve here, to the underside of the liver, where its attachment is just out of sight.
It's attached up here to the underside of the diaphragm. The lesser omentum extends down here onto the duodenum, where it has a free lower border as we'll see.
Behind the lesser omentum, which we'll divide along this line, we come into an extensive back-pocket of the peritoneal cavity, the omental bursa or lesser sac, that continues around behind the stomach. We'll see more of it later.
To see the greater omentum we'll go to an earlier stage in the dissection. All this is the greater omentum. We'll pick it up to see its free lower border. Here's part of its attachment to the greater curve of the stomach. Between its peritoneal layers there's a variable amount of fat. On the front, the greater omentum hangs free, in front of the coils of small intestine. On the back, it's attached to the front of the transverse colon.
The part of the greater omentum between the stomach and the transverse colon is called the gastro-colic ligament. If we divide it, which we've done here, we come again into the lesser sac, this time below the stomach.
We're looking at some puzzling structures! To understand why they're arranged as they are, it'll be helpful to see how they developed.