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The Organs of Circulation.The heart is a mass of muscle so arranged as to surround two cavities which communicate with the arteries and veins of the body. It is shaped somewhat like an inverted cone, and is placed in the chest a little to the left and behind the breastbone, between the third and the seventh ribs. The greater part of it is covered by the left lung, which intervenes between the heart and the ribs. The heart is enclosed in a membranous sac called the pericardium. The weight of the heart in adults is eight or nine ounces, being usually about an ounce heavier in man than in woman. The blood is brought to the right cavity of the heart by the veins of the body, and is propelled by the muscular wall of this cavity into the lungs, where it is purified by contact with the air and returned to the left side of the heart. The large and powerful muscle surrounding the left cavity of the heart drives the blood through the arteries into the different parts of the body. This action of the heart in pumping the blood through the body consists of a series of beats, or pulsations, which ordinarily occur from seventy to eighty times per minute ; hence the heart beats more than 100,000 times every twenty-four hours. The Arteries-are strong, elastic tubes or channels which conduct the blood from the heart to all parts of the system. The left side of the heart is continuous with a large artery called the aorta, into which all the blood of the body passes. This artery divides and gives off branches whereby the blood is conducted to all the different organs. These arteries in turn divide into smaller branches, and finally terminate in a series of delicate tubes called capillaries, so called because of their small, kair-like size. The fact is, that they are far more minute than hairs. The blood passes through these capillaries into the tubes which are continuations of them, called veins. These veins unite to form larger trunks, and are finally combined into two large veins which empty into the right side of the heart. But first, if you want to come back to this web site again, just add it to your bookmarks or favorites now! Then you'll find it easy! Also, please consider sharing our helpful website with your online friends.
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