Twelfth rib

Last revised by Craig Hacking on 12 Oct 2020

The twelfth rib is an atypical rib. It is the shortest rib, and one of two floating ribs.

The 12th rib has a single facet on its head for articulation with the T12 vertebra. It has a short neck and no tubercle. It also lacks a costal groove and angle. internal surface of this word about slopes slightly upwards. 

The pointed anterior end of the 12th rib is covered with costal cartilage. Its length is highly variable.

  • quadratus lumborum: anterior inferior surface on the medial half
  • internal intercostal muscle: medially at or near the upper border of the anterior surface
  • external intercostal muscle: the upper border of the external surface
  • diaphragm: laterally at or near the upper border
  • lumbocostal ligament: posteriorly, near the head, running to the first lumbar transverse process
  • levator costae: external surface medially
  • longissimus thoracis: external surface medially
  • iliocostalis: external surface medially
  • serratus posterior inferior: external surface laterally
  • latissimus dorsi: external surface laterally
  • external oblique: external surface laterally

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Cases and figures

  • Figure 1: atypical ribs - 10, 11, 12 (Gray's illustration)
    Drag here to reorder.
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