(3.05)
The last organ we'll look at, that lies within the abdominal cavity, is the spleen. Functionally the spleen doesn't have anything to do with the GI tract, but it does have peritoneal connections to the stomach and other viscera.
In the living body the spleen is here, well above the left costal margin. The ninth, tenth and eleventh ribs overlie it. To see the spleen we'll go back to this dissection, in which the lower ribs have been removed, and the diaphragm stretched flat, and stitched to the cut edge of the chest wall.
Here's the spleen, lying between the stomach and the rib cage. The spleen is an important filter of blood cells, and a significant component of the immune system. It's covered by peritoneum, except here at its hilum, where the splenic blood vessels enter.
This sheet of peritoneum, the gastro-splenic ligament, extends to the greater curve of the stomach. It's in fact an upward continuation of the greater omentum. If we divide the gastrosplenic ligament, which we've done here, we come into the lesser sac, which is no surprise when we recall the developmental anatomy here.
You'll recall that the spleen developed between the two layers of the dorsal mesogastrium. As it grew it bulged out within the outer layer, which forms its peritoneal covering.
Two double folds of peritoneum meet at the hilum: one in front, the gastrosplenic ligament which we just divided, and one behind, the lieno-renal ligament, which we haven't seen yet. Between the two folds is the left-hand limit of the lesser sac.
Going back to the to the dissection, here's the divided gastrosplenic ligament, here behind the spleen is the lieno-renal ligament. This gives the spleen a loose connection to the left kidney, which lies just behind it. Here in the posterior wall of the lesser sac, the tail of the pancreas comes almost to the hilum of the spleen.
The left flexure of the colon, the splenic flexure, lies in front of the spleen and just below it. Here in a different specimen is the same area seen from the left side. The lower ribs came down to here. As before, we've stitched the cut edge of the diaphragm to the chest wall, all the way along here.
Here's the spleen, with the diaphragm right behind it. Here's the splenic flexure and the descending colon. Here's the edge of the liver, here's the greater curve of the stomach, here's the gastrosplenic ligament, continuous here with the dependent greater omentum.