Rib 4 (left) — true rib

Function

Mid-cage rib shielding the heart's left border and the lung's oblique fissure; its intercostals drive the bucket-handle breathing motion.

Landmarks

• Costal groove
• Angle
• Tubercle

Articulations (joints)

• T3–T4 vertebrae
• Sternum via fourth costal cartilage

Clinical relevance

The fourth or fifth intercostal space in the mid-axillary line (the 'safe triangle') is the standard chest-drain site.