The gastro-hepatic omentum, (Fig. XIX, 16.) passing upwards from the lesser curvature of the stomach to the transverse fissure of the liver, presents a free edge, which looks downwards and to the right, and which forms the anterior boundary of the foramen of Winslow, the channel of communication between the greater and the lesser peritoneal sacs. (Fig. XIX, 17.)
The free edge of this omentum further contains (between its two layers of peritoneum) three important structures :
1. The common bile-duct to the right.
2. The hepatic artery to the left.
3. The portal vein behind and between the two former structures.
In mapping out any of these structures, it is, therefore, advisable to first draw in the lesser curvature of the stomach, the pylorus, the three parts of the duodenum, and the pancreas. The pylorus occupies such a definite position in the transpyloric plane that all these structures are easily and quickly drawn in. The free margin of the lesser omentum should be represented as a curved line passing upwards and to the right for 1 1/2 to 2 inches from the duodeno-pyloric junction. The portal vein is formed behind the head of the pancreas by the union of the superior mesenteric and splenic veins, and passes upwards to the transverse fissure of the liver behind the first part of the duodenum, and in the free edge of the lesser omentum.
The hepatic artery, a branch of the coeliac axis, passes upwards from the upper border of the first part of the duodenum, in the free edge of the lesser omentum, to the transverse fissure of the liver.
The common bile-duct is 3 inches long, and is formed by the union of the hepatic and cystic ducts. (Fig. XIX, 18.)
It passes downwards in the free edge of the gastro-hepatic omentum, behind the first part of the duodenum, behind the head of the pancreas, and opens on the inner and posterior aspect of the second or descending part of the duodenum.
The long axis of the spleen corresponds to the tenth rib,(Fig. XVII, 9.) and the viscus extends upwards to the upper border of the ninth rib, and downwards to the lower border of the eleventh rib. The upper and inner pole lies 1 1/2 to 2 inches away from the tenth dorsal spine, whilst the lower or anterior pole reaches as far forwards as the mid-axillary line.