The first, second, tenth, eleventh and twelfth ribs are considered atypical ribs because of their specific characteristics.

First rib

The first rib is the shortest, widest and has the sharpest curve of all the ribs. There is only one articular surface on the head of the first rib for articulation with the body of the first thoracic vertebra.

The tubercle of the first rib is like that of typical ribs, as it has a facet for articulation with the transverse process of the corresponding vertebra.

The first rib has distinct features on the superior surface - two grooves for the subclavian vessels. These grooves are separated by the scalene tubercle, which is the attachment site for the anterior scalene muscle.

Second rib

The second rib is thinner and significantly longer than the first rib. There are two articular facets on the head of the second rib for articulation with the first thoracic (T1, superior) and second thoracic (T2, corresponding) vertebrae.

The main distinguishing feature of the second rib is a roughened tuberosity on its superior surface, which provides part of the origin for the serratus anterior muscle.

Tenth, eleventh, twelfth ribs

The heads of the tenth, eleventh, and twelfth ribs have only one facet, because they each articulate with only one vertebra. The eleventh and twelfth ribs in particular are short and have no necks or tubercles.

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Atypical ribs