The
projection demonstrates mediastinal divisions into the superior, anterior,
middle and posterior. Note the backwards slant of the trachea from the thoracic
inlet to the carina. This slant should be borne in mind when tracheal tomograms
are performed. Note the position of the outflow tract of the right ventricle
and the high position of the left atrium. Note the position of the lung
fissures, the left oblique fissure reaching its inferior limit about 5 cm
behind the sternum. The right oblique fissure travels more anteriorly at its
lower limit. Note also the apparently translucent anterior mediastinum in the
normal.
