Chapter 7
The Skeleton
225
7
attachment points for many muscles of the neck, back, chest, and
shoulders. Te
intercostal spaces
between the ribs are occupied by
the intercostal muscles, which liF and then depress the thorax dur-
ing breathing.
Sternum
Te
sternum
(breastbone) lies in the anterior midline of the tho-
rax. Vaguely resembling a dagger, it is a flat bone approximately
15 cm (6 inches) long, resulting from the fusion of three bones: the
manubrium, the body, and the xiphoid process. Te
manubrium
(mah-nu
9
bre-um; “knife handle”) is the superior portion, which
is shaped like the knot in a necktie. Te manubrium articulates
via its
clavicular notches
(klah-vik
9
u-lar) with the clavicles (col-
larbones) laterally, and just below this, it also articulates with the
first two pairs of ribs. Te
body
, or midportion, forms the bulk of
the sternum. Te sides of the body are notched where it articu-
lates with the costal cartilages of the second to seventh ribs. Te
xiphoid process
(zif
9
oid; “swordlike”) forms the inferior end of the
sternum. Tis small, variably shaped process is a plate of hyaline
cartilage in youth, but it is usually ossified in adults over the age of
40. Te xiphoid process articulates only with the sternal body and
serves as an attachment point for some abdominal muscles.
Homeostatic Imbalance
7.4
In some people, the xiphoid process projects posteriorly. In such
cases, blows to the chest can push the xiphoid into the underly-
ing heart or liver, causing massive hemorrhage.
Te sternum has three important anatomical landmarks: the jugu-
lar notch, the sternal angle, and the xiphisternal joint (±igure 7.23).
Te easily palpated
jugular
(
suprasternal
)
notch
is the central in-
dentation in the superior border of the manubrium. If you slide your
finger down the anterior surface of your neck, it will land in the jugu-
lar notch. Te jugular notch is generally in line with the disc between
the second and third thoracic vertebrae and the point where the
leF common carotid artery issues from the aorta (±igure 7.23b).
Intercostal
spaces
Xiphisternal
joint
Heart
Sternal angle
Jugular notch
True
ribs
(1–7)
False
ribs
(8–12)
Jugular notch
Clavicular notch
Manubrium
Sternal angle
Body
Xiphisternal
joint
Xiphoid
process
L
1
Vertebra
Floating
ribs
(11, 12)
(b) Midsagittal section through the thorax, showing
the relationship of surface anatomical landmarks
of the thorax to the vertebral column
(a) Skeleton of the thoracic cage, anterior view
T
2
T
4
T
3
T
9
Sternum
Costal cartilage
Costal margin
Figure 7.23
The thoracic cage.
(For a related image, see
A Brief
Atlas of the Human Body
, Figure 23a–d.)
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