of the Human Heart
The outer covering of
the heart is a strong, thin membrane called the pericardium.
The superior vena cava,
aorta, and other large
blood vessels lead in and out of the heart.
Smaller blood vessels nourish the heart itself.
The ventricles make
up the largest part of the heart. They form the
whole lower portion. Their thick, strong muscles
pump blood throughout the body.
The atria form the
upper, smaller part of the heart. They have thin
walls, and are smaller than the ventricles. Each
atrium serves as a collecting station for the
blood that flows into the heart.
The World Book Encyclopedia
Chicago: World Book-Childcraft International,
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