Thorax and Abdomen

Here the organs in the thoracic and abdominal cavities have been exposed. The midventral strip of tissue lying between a pair of lateral incisions contains the umbilical arteries, urinary bladder, and, in the male, the penis. Notice the remains of the muscular diaphragm that forms a more or less transverse partition between the abdominal and thoracic cavities. In this image, it has been cut to open the cavitites.

The body cavity in which the thoracic and abdominal organs are situated is called the coelom. It is completely lined with a shiny coelomic epithelium which also covers all of the internal organs. In life, a bit of fluid within the coelom facilitates the expansion, contraction, and other functional movements of the organs.

The part of the coelom anterior to the diaphragm is divided into three parts. There are two lateral pleural cavities, each of which contains one of the lungs. Between the pleural cavities is the pericardial sac (visible in 'more images'), which contains the heart. The pericardial sac may be partly covered by the thymus.

The portion of the coelom posterior to the diaphragm is the peritoneal cavity. The epithelial lining of this cavity (shown in the inset) is referred to as the peritoneum. The peritoneum covers both the walls of the cavity (parietal peritoneum) and the viscera themselves (visceral peritoneum). The viscera are suspended from the body wall by folds of peritoneum called mesenteries. The blood vessels which supply the organs pass through these mesenteries.