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To verify the inferior extent of this the costodiaphragmatic recess, identify the 9th intercostal space (ICS) in the mid-axillary line and pass a probe horizontally through the chest wall at this level. As you do this, review the layers of the chest wall through which the probe passes. This site is clinically important because it can be used to safely drain excess fluid from the pleural cavities during thoracocentesis.

Links and References:
Grant's: 1.28
Netter: 186
Rohen/Yokochi: 249, 250