Section IV—Pleuroperitoneal Cavity and Viscera
Dissection of the pleuroperitoneal cavity in Necturus allows examination of both digestive and urogenital structures. Many vessels will also be noted at this time. Enter the pleuroperitoneal cavity by making a longitudinal incision about 0.5 cm to the left of the midventral line.
If the vessels of your specimen have been injected, its abdominal wall will have been cut. If so, continue along this cut to expose the cavity. Cut anteriorly until you reach the level of the posterior margin of the forelimbs, at which point you will have reached the posterior margin of the coracoid cartilage. Cut posteriorly to the posterior margin of the hindlimbs, cutting through the puboischiadic plate.Gently spread the abdominal wall (Figure 5.11). The large, elongated, dark structure midventrally is the liver. Lift the cut edge of the body wall to observe the falciform ligament extending between the wall and the ventral surface of the liver. The ligament is much larger than in the other vertebrates considered here. Note the ventral abdominal vein passing along the midventral abdominal wall and toward the liver through the free posterior margin of the ligament. Examine the pos- teroventral part of the cavity to observe the thin-walled
FIGURE 5.11 Pleuroperitoneal cavity of the mudpuppy in ventral view.
urinary bladder. It is supported from the midventral abdominal wall by the median ligament. A vesicular vein from the bladder passes in the anterior free margin of this ligament to join the ventral abdominal vein.
Carefully cut through the falciform ligament, and make two transverse cuts through the body wall, one on either side, to create four flaps that can be spread apart. (Much of the ventral body wall has been removed in Figures 5.12-5.14, but you need not do so to observe the following structures.) The long, light-colored, tubular stomach (Figure 5.11) lies dorsal and slightly to the left of the liver.
Lift the stomach to see that it is supported by the greater omentum. Spread apart the liver and stomach. The gastrohepatic ligament is the small, triangular sheet stretching between their anterior portions (Figure 5.12).The elongated spleen hangs from the posterior left side of the stomach (Figures 5.11 and 5.12). The gastrosplenic ligament extends between these organs (Figure 5.12). The stomach ends abruptly at the pyloric sphincter, a marked constriction beyond which the digestive tract continues as the long, coiled small intestine, followed by the short, straight large intestine. The mesentery supports the small intestine. Spread the coils of the small intestine to observe it. The mesorectum supports the large intestine (Figure 5.12).
The first loop of the small intestine is the duodenum (Figures 5.11 and 5.12). The hepatoduodenal ligament extends between the duodenum and the dorsal surface of the liver (Figure 5.12). Several organs and vessels lie in this region, but may be difficult to discern. Examine this region in several views as follows, referring to Figures 5.12-5.14. The pancreas lies along the duodenum (and partly within the hepatoduodenal ligament). To help identify it, pull the stomach to the left and reflect the liver to the right to expose its dorsal surface (Figure 5.12). The pancreas is irregular, but note that part of it extends anteriorly toward the spleen. The gastrosplenic vein lies partly embedded within this lobe and extends toward the spleen.
Observe the long, thin transparent left lung lying dorsal to the stomach. The right lung is similar in form. Look between the stomach and the liver. You should discern the right and left lungs, apparently lying side by side. For now, distinguish between them but do not tear through any mesenteries. The liver is supported anterodorsally by the hepatocavopulmonary ligament. The posterior vena cava is the large vessel passing through the posterior end of this ligament (Figure 5.12).
Note the large hepatic portal vein embedded in the dorsal part of the liver.Next, reflect the stomach to the right, so that it lies on the liver’s dorsal surface, as shown in Figure 5.13. Note the relationships among the liver, stomach, spleen, and pancreas, as well as their associated mesenteries. Lift the left lung. It is supported by a narrow pulmonary ligament, which is connected to the greater omentum.
Next, let the viscera fall back in place, and then reflect the liver to the left, as shown in Figure 5.14. Examine the posterodorsal part of the liver for the gall bladder, a thin, translucent, greenish sac. Gently lift it and examine the region where it attaches to the liver. The cystic duct leaves the gall bladder but is joined by several (and usually fairly narrow) hepatic ducts from the liver to form the common bile duct, which passes partly through the substance of the pancreas to reach the duodenum. The bile duct is similar to that of the shark and cat, but is much shorter. Note again the positions of the posterior vena cava and gastrosplenic vein. Examine the right lung. Its pulmonary ligament, wider than that of the left lung, is part of the hepatocavopulmonary ligament.
Key Terms: Pleuroperitoneal Cavity and Viscera
common bile duct cystic duct duodenum falciform ligament gall bladder gastrosplenic vein gastrohepatic ligament gastrosplenic ligament greater omentum hepatic ducts hepatic portal vein hepatocavopulmonary ligament hepatoduodenal ligament large intestine
liver
lung median ligament mesentery mesorectum
pancreas posterior vena cava pulmonary ligament pyloric sphincter small intestine
spleen stomach urinary bladder ventral abdominal vein vesicular vein