First rib

At a glance

English

First rib

Latin (TA2)

Costa prima

System

Bone

Region

Thorax

Side

Paired, left and right

Series

Ribs

Muscles on it

Longissimus thoracis

About the first rib

The first rib is the highest rib, sitting just beneath the clavicle at the root of the neck. It is the most sharply curved of the series and usually the shortest. Unlike the ribs below it, it lies almost flat, so one surface faces up and the other down, with one border looking inward and the other outward. It is a true rib, joined at the front to the manubrium of the sternum by its costal cartilage.

At the back, the small rounded head carries just one facet, which meets the T1 vertebral body alone. A short, narrow neck leads to a thick tubercle on the outer border that articulates with the T1 transverse process. No angle is present; instead the rib bends gently at the tubercle so that the head points downward. No other rib has so broad and thick a front end.

The upper surface is the part students remember. Two shallow grooves cross it, divided by a low ridge that runs to the scalene tubercle on the inner border, where the scalenus anterior attaches. The subclavian vein passes in the groove in front of the tubercle; the groove behind it carries the subclavian artery together with the inferior trunk of the brachial plexus. Further back, a roughened area takes the scalenus medius. The lower surface is smooth and has no costal groove. The convex outer border, near its back end, gives origin to the first slip of serratus anterior.

Because the artery, vein and nerve trunk cross this rib on their way to the arm, the first rib is central to thoracic outlet problems, where these structures are squeezed between the rib, the scalene muscles and the clavicle.

Function and supply

Function

Forms the upper rim of the thoracic inlet, anchors the scalene muscles that raise it in deep breathing, and carries the subclavian vessels and brachial plexus towards the arm.