Twelfth rib

Costa fluitans XII

SkeletalSkeletonAbdomenLeft and right

View left in 3D View right in 3D

What it is
The twelfth rib, a floating rib: a curved flattened bar whose head articulates with T12, its tubercle with the T12 transverse process, sloping down and forward to its costal cartilage.
Function
Protects the thoracic organs and moves up and out with the intercostal muscles during breathing (bucket-handle motion).
Size
Cross-section ≈ 6 × 11 mm; arc length ≈ 17 cm
Clinical note
Floating ribs end free in the flank muscles and have no anterior attachment.

Nearby skeletal structures Intervertebral disc L1–L2, Intervertebral disc L2–L3, Intervertebral disc L3–L4, Intervertebral disc L4–L5, L1 vertebra, L2 vertebra, L3 vertebra, L4 vertebra, L5 vertebra, Twelfth costal cartilage