costal pleura reflects onto the diaphragm above the costal margin. in the MIDCLAVICULAR line, the pleural cavity extends inferiorly to approximately RIB 8. in the MIDAXILLARY line, it extends to RIB 10. from this point, the inferior margin courses somewhat horizontally crossing RIBS 11 & 12 to reach VERTEBRA T12. from the midclavicular line, the inferior boundary of the pleura can be approximated by a line that runs between RIB 8, RIB 10, and VERTEBRA T12