Page 43 - Clinical Anatomy

ECA1 7/18/06 6:31 PM Page 28

28 The Thorax

bronchus which is absent on the left, the lower lobes being otherwise mirror
images of each other.

The mediastinum

The mediastinum is defined as ‘the space which is sandwiched between the
two pleural sacs’. For descriptive purposes the mediastinum is divided by a
line drawn horizontally from the sternal angle to the lower border of T4
(angle of Louis) into superior and inferior mediastinum. The inferior medi-
astinum is further subdivided into the anterior in front of the pericardium,
a middle mediastinum containing the pericardium itself with the heart and
great vessels, and posterior mediastinum between the pericardium and the
lower eight thoracic vertebrae (Fig. 22).

The pericardium

The heart and the roots of the great vessels are contained within the conical
fibrous pericardium, the apex of which is fused with the adventitia of the

Fig. 22◊The subdivisions
of the mediastinum.