The stomach begins as a dilation of the foregut. The dorsal surface grows faster than the ventral surface. This, combined with breakdown of cells in the dorsal mesentery (dorsal mesogastrium) results in rotation of the stomach around its longitudinal axis as well as around its anteroposterior axis.

The original dorsal surface becomes the greater curvature, the original ventral surface becomes the lesser curvature and the original left surface is anterior.

The left surface of the stomach comes to face anteriorly, so the left vagus nerve becomes the anterior vagus nerve.

Note that the greater omentum, derived from the dorsal mesogastrium hangs from the greater curvature of the stomach.

The duodenum has dual origin from both the foregut and midgut, and as such, has blood supply from both the celiac and superior mesenteric arteries.

The foregut derived part of the duodenum includes the superior part, and about 1/2 of the descending part, up to and including the major duodenal papilla.

The remainder of the descending part, the horizontal part and the ascending part are from the midgut.

The horizontal dashed line marks the division between foregut and midgut derived parts of the duodenum
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The liver appears in the middle of the 3rd week of development as a ventral outgrowth of the foregut endoderm.
The parenchyma of the liver is derived from the endoderm of the foregut and it maintains a connection to the developing duodenum through the common bile duct.
The ventral pancreatic bud and diverticulum of the gallbladder also arise from the common bile duct.
The liver bud grows into and divides the ventral mesentery of the foregut into two parts.

In the 5th week, the liver bud continues to grow into the ventral mesentery. It also grows cranially toward the septum transversum, a plate of mesoderm that separates the developing thoracic cavity and developing abdominal cavity and which will contribute to the development of the diaphragm. This divides the ventral mesentery into two parts: falciform ligament and lesser omentum.

By the 6th week, the liver has separated the layers of the ventral mesentery to form the capsule of the liver. It has also grown cranially into the septum transversum and where the liver contacts the septum transversum, there is no peritoneum on the surface which becomes the bare area of the liver. The liver divides the ventral mesentery into the lesser omentum which connects the liver to the lesser curvature of the stomach and the 1st part of the duodenum. It has two parts, the hepatogastric and hepatoduodenal ligaments. The portion of the ventral mesentery that attaches the liver to the anterior body wall is the falciform ligament.

The pancreas begins in the 4th week of development as a pair of endodermal outgrowths from the foregut.
The dorsal pancreatic bud arises directly from the foregut.
The ventral pancreatic bud is an outgrowth of the bile duct.

For this reason, the bile duct and pancreatic duct open together in the wall of the duodenum.

Endoderm gives rise to the pancreatic acinar cells and the lining cells of the pancreatic ducts. The pancreatic acinar cells produce digestive enzymes that are secreted into the duodenum.

The pancreatic islets form the endocrine portion of the pancreas and secrete hormones that regulate the metabolism of the carbohydrates. The pancreatic islets are derived from neural crest cells.

The ventral pancreatic bud contributes to the inferior portion of the head and the uncinate process of the pancreas. The dorsal bud gives rise to the superior part of the head, the body and the tail of the pancreas. The duct system comes from the ducts of both buds. The proximal part of the duct, including the portion contributing to the major duodenal papilla comes from the duct of the ventral bud. The distal part of the duct is derived from the dorsal bud. The original attachment of the dorsal bud is usually lost, but may persist as an accessory pancreatic duct. The pancreatic islet cells are thought to be derived from neural crest cells.

When first formed, the gut tube is attached to both the posterior and anterior body wall by a dorsal mesentery (posterior) and a ventral mesentery (anterior).

The dorsal mesentery persists along the entire length of the gut tube but the ventral mesentery persists only in the region of the foregut.

Growth of the liver as a ventral diverticulum of the foregut divides it into the falciform ligament, the mesentery between the liver and anterior body wall and the lesser omentum, the mesentery between the liver and lesser curvature of the stomach.

Rotation of the stomach around its longitudinal axis displaces the liver to the right and the spleen to the left and separates a small part of the peritoneal cavity to be contained posterior to the stomach. This is the lesser sac.

A sagittal view shows that the rotation of the stomach also produces a redundancy of the dorsal mesentery that hangs down from the greater curvature of the stomach. This double fold of mesentery becomes the greater omentum.