Figure 4-5. The human thorax with bones of the shoulder region.
(1) The sternum lies in the midline of the thorax anteriorly. It is made up of
three parts: the manubrium at the top, the body as the main part, and the xiphoid
process below. On the top of the manubrium is the jugular (sternal) notch, a common
landmark. The junction between the manubrium and the body is a joint called the
sternal angle. This sternal angle is an important landmark clinically because the second
rib attaches to the sternum at this junction. It is just a matter of simple counting after
identifying the second rib to know where you are on the thoracic wall.
(2) The rib cage consists of the 12 thoracic vertebrae, 12 pairs of ribs, and
the sternum. Each rib is curved laterally from back to front. All 12 pairs of ribs are
attached posteriorly to the thoracic vertebrae. The upper six pairs of ribs are attached
directly to the sternum by their costal cartilages. The seventh through tenth pairs of ribs
are attached indirectly to the sternum through their costal cartilages (by attaching to the
costal cartilage of the rib above). Rib pairs 11 and 12 do not attach to the sternum.
Instead, they are embedded in the trunk wall muscles.
c. The Skull. The skull (figure 4-6) is the bony framework (skeleton) of the head
region. It has two major subdivisions: the cranium which encases and protects the
brain and the facial skeleton which is involved with the beginnings of the digestive and
respiratory systems. The special sense organs (eyes, ears, etc.) are included and
protected within the skull.