The manubrium and body of the sternum lie in diF
erent planes, so
their line of union projects slightly forward. This projection, at the
level of the second costal cartilage, is called the sternal angle (angle
of Louis). It is commonly used as a clinical landmark to locate a par-
ticular rib (see ±
bre-um), a middle
that projects downward (see
F g. 7.38).
The sides of the manubrium and the body are notched
where they articulate with costal cartilages. The manubrium
also articulates with the clavicles by facets on its superior
border. It usually remains as a separate bone until middle
age or later, when it fuses to the body of the sternum.
The thoracic cage
) the thoracic vertebrae,
the sternum, the ribs, and the costal
cartilages that attach the ribs to
the sternum. (
) Radiograph of the
thoracic cage, anterior view. The
light region behind the sternum and
above the diaphragm is the heart.