The eleventh and twelfth ribs typically have no neck.
Here's a breakdown:
Ribs are categorized as true, false, and floating, based on their connection to the sternum. The structural features of ribs can vary slightly, especially among the lower ribs.
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Typical Ribs (3rd-9th): These ribs have a head, neck, tubercle, and shaft. The head articulates with the vertebral bodies, and the tubercle articulates with the transverse process of a vertebra.
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Atypical Ribs: These ribs have variations in their structure:
- 1st Rib: Shorter and wider than other ribs.
- 2nd Rib: Thinner and longer than the first rib, with a tuberosity for the serratus anterior muscle.
- 10th Rib: Has only one facet on its head for articulation with a single vertebra.
- 11th and 12th Ribs: Often have only one facet on their head and lack a neck and tubercle. They are also shorter and have pointed ends. These are the "floating ribs."
Therefore, the eleventh and twelfth ribs are the ones that typically lack a neck. They also often lack a tubercle. Their simplified structure is related to their floating nature (not being attached to the sternum).
