Human Anatomy Vol 1

Thorax (Latin chest) forms the upper part of the trunk

of the body. It not only permits boarding and lodging

of the thoracic viscera, but also provides necessary

shelter to some of the abdominal viscera.

The trunk of the body is divided by the diaphragm

into an upper part, called the thorax, and a lower part,

called the abdomen The thorax is supported by a skeletal

framework, thoracic cage. The thoracic cavity contains

the principal organs of respiration-the lungs and of

circulation-the heart both of which are vital for life.

Bony Londmorks

I Suprasternal or jugular notch (Fig. 12.1): It is felt just

above the superior border of the manubrium

between the sternal ends of the clavicles. It lies at

the level of the lower border of the body of the second

thoracic vertebra. The trachea can be palpated in this

notch.

2 Sternal angle/angle of Louis: It is felt as a transverse
ridge about 5 cm below the suprasternal notch. It
marks the manubriosternal join! and lies at the level
of the second costal cartilage anteriorly, and the
disc between the fourth and fifth thoracic vertebrae
posteriorly. This is an important landmark for the
following reasons.
a. The ribs are counted from this level downwards.
There is no other reliable point (anteriorly) from
which the ribs may be counted. The second costal
cartilage and second rib lie at the level of the
sternal angle or angle of Louis (French physician
1787-1872). The ribs are counted from here by
tracing the finger downwards and laterally
(because the lower costal cartilages are crowded
and the anterior parts of the intercostal spaces are
very narrow).

b. It marks the plane which separates the superior

mediastinum from the inferior mediastinum.

c. The ascending aorta ends at this level.

d. The arch of the aorta begins and also ends at this

level.

e. The descending aorta begins at this level.

f. The trachea divides into two principal bronchi.

g. The azygos vein arches over the root of the right

lung and opens into the superior vena cava.

h. The pulmonary trunk divides into two pulmonary

arteries just below this level.

i. The thoracic duct crosses from the right to the left

side at the level of the fifth thoracic vertebra and

reaches the left side at the level of the stemal angle.

j. It marks the upper limit of the base of the heart.

k. The cardiac plexuses are situated at the same level.

3 Xiphisternnl joint: The costal margin on each side is

formed by the seventh to tenth costal cartilages.

Between the two costal margins, there lies the

First rib

Suprastemal notch

Manubrium

lntercostal space

Body of sternum

Costal cartilages

Ribs

Xiphisternal joint

Xiphoid process

Fig. 12.1: Shape and construction of the thoracic cage as seen

from the front