The first rib is atypical. It is
found to be short, flat and more sharply curved than any of the others. It
has upper and lower surfaces, with outer and inner borders, and on its head
there is one articular facet only.
The upper surface has two grooves for the
subclavian artery and subclavian vein, separated by the scalene tubercle for
the attachment of the scalene anterior muscle.
This rib has very little movement during
respiration and serves as a base attachment for the intercostal muscles and
the ribs below. In other words, during respiration, the muscles in the first
intercostal space contract, drawing up on the rib below, which in turn
allows its muscles to pull up on the rib below it and so forth, until all
ribs have moved through a small distance. The combined movements increase
the transverse and anteroposterior diameters of the thoracic cavity.
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