In this laboratory the pleural cavities and the lungs will be studied. The pleural cavities are lined by a continuous membrane, called pleura, which covers the surface of the lungs and the adjacent surfaces of the walls surrounding them. The portion of the pleura that covers the lungs is called visceral pleura. The walls of each pleura cavity are lined with parietal pleura.
An important part of this exercise will be exploring the pleural cavities and determining their boundaries. The extent of the pleural cavities can be defined in relation to the rib levels. Each pleural cavity extends to the eighth rib in the midclavicular plane, the tenth rib in the midaxillary plane, and the twelfth rib near the vertebral column. During quiet or even forced respiration, the borders of the lungs do not extend to the inferior extent of each pleural cavity (Figure 19.1). The spaces into which the lungs do not extend are called pleural recesses. They will be examined during this exercise.