Abdominal cavity

The abdominal cavity is the largest internal space of the trunk, bounded cranially by the diaphragm, dorsally by the lumbar vertebrae, ventrally and laterally by the abdominal muscles, and caudally by the pelvic inlet. It is not physically separated from the pelvic cavity, with which it freely communicates.

It contains and protects most of the organs of the digestive, urinary, and endocrine systems, as well as the spleen. This space is lined by a serous membrane, the peritoneum, which produces a small amount of lubricating fluid to allow the organs to move freely. The peritoneum is divided into parietal peritoneum (lining the walls), visceral peritoneum (covering the organs), and connecting peritoneum (mesenteries, omenta, and ligaments), which suspend the organs and serve as pathways for vessels and nerves.

The abdominal cavity shows interspecies differences, mainly dictated by diet and posture. In ruminants, the multi-compartment stomach (rumen, reticulum, omasum, abomasum) occupies most of the left abdominal cavity, whereas the horse, a monogastric herbivore, is characterized by an extremely developed and complex cecum and colon that fill a large portion of the caudal and right abdomen. In contrast, the dog, cat, and human have a simple stomach and a proportionally less voluminous digestive tract.