We'll look at a specimen in which the full thickness of the anterior abdominal wall has been removed, from an area bounded on each side by the costal margin, the mid-axillary line, and the inguinal ligament.
This presents us with a complex spectacle that we'll soon begin to understand, but first we'll focus on the important lining layer of the abdominal cavity, the peritoneum. Here round the edge, we've left a fringe of peritoneum intact. Peritoneum is a thin serous membrane, quite similar to pleura. It provides a continuous lining for the abdomino-pelvic cavity.
To understand the shape and extent of the cavity we're gettting into, we'll look at a specimen in which all the abdominal organs have been removed.
From in front we don't see the whole of the abdominal cavity. There's much more of it up here, above the costal margin and beneath the diaphragm. All this is the diaphragm. This upper part of the abdominal cavity, which extends up to this line, contains almost all of the liver, most of the stomach, and the spleen.
Down here, we're looking into the pelvic cavity, which extends backwards and downwards. It's quite a small space. The pelvic brim, which is here, marks the arbitrary boundary between the abdominal and pelvic cavities.
In the midline, this massive projection is created by the bodies of the lumbar and lower thoracic vertebrae. It divides the posterior part of the abdominal cavity from top to bottom into two deep valleys. This shiny layer is parietal peritoneum. In this dissection all the parietal peritoneum in this central area has been removed. Its attachments in this area are quite complex, as we'll see.
The surfaces of the organs that lie within the abdominal cavity are also covered with a continuous layer of peritoneum. The visceral layer of peritoneum that covers the organs is continuous with the parietal layer that lines the cavity.
The space between adjoining peritoneal surfaces is normally occupied by just a trace of serous fluid. Those organs that lie freely mobile within the abdominal cavity, like the small intestine here, are attached to the wall of the cavity by double sheets of peritoneum, in which their blood vessels run.
As we progress, we'll see how the various peritoneal folds and attachments are arranged, and we'll get an appreciation of the complexities of the peritoneal space.