CHAPTER VII.

PHYSIOLOGICAL ANATOMY.

CIRCULATORY ORGANS.


Having considered the formation of chyle, traced it through the
digestive process, seen its transmission into the _vena cava_, and,
finally, its conversion into blood, we shall now describe how it is
distributed to every part of the system. This is accomplished through
organs which, from the round of duties they perform, are called
_circulatory_. These are the Heart, Arteries, Veins, and Capillaries,
which constitute the _vascular system_.

Within the thorax or chest of the human body, and enclosed within a
membranous sac, called the _pericardium_, is the great force-pump of the
system, the heart. This organ, to which all the arteries and veins of
the body may be either directly or indirectly traced, is roughly
estimated to be equal in size to the closed fist of the individual to
whom it belongs.

It has a broad end turned upwards, and a little to the right side,
termed its _base_; and a pointed end called its _apex_, turned
downwards, forwards, and to the left side, and lying beneath a point
about an inch to the right of, and below, the left nipple, or just below
the fifth rib. Attached to the rest of the body only by the great
blood-vessels which issue from and enter it at its base, the heart is
the most mobile organ in the economy, being free to move in different
directions.