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PHYSIOLOGY AND ANATOMY. BS 
The letter a is the left ventricle; b, is the right ventricle ; 
¢, ¢, f, is the great artery that proceeds from the left ventri- 
cle ; g, h, i, are arteries that proceed from the great artery; 
&, is the artery that goes from the right ventricle to the lungs ; 
l, 1, are branches of the artery going to the two sides of the 
lungs, which carry the blood there; m, m, the veins which 
bring the blood back from the lungs to the left side of the. 
heart ; n, is the right auricle ; » and p, are the ascending and 
descending veins, which meet and form the right auricle; p, _ 
represents the veins from the liver, spleen, and bowels ; $1 is - 
the left artery, one which nourishes the heart. 
The heart has four divisions—two to receive the blood after 
it is made from the food, called auricles, and two others, call- 
ed ventricles, to send it to the several stations where it is most 
needed. After the blood comes to the heart from the veins, 
it is necessary to send it to the lungs before it is fit for use. 
For this purpose there are muscles in the heart which con- 
tract and force it out to the lungs. Motion is of two kinds: 
voluntary and involuntary. That is voluntary which is per- 
formed by means of the bones, muscles, and tendons, and is _ 
influenced by the will or mind. Involuntary motion is that 
produced by organs not connected with the bones, but which 
possess muscular fibres ; as, for instance, the stomach, which 
is a hollow muscle and dieses its food without the knowl- 
- edge of the mind. The heart is also a hollow muscle, which 
contracts and expands to receive and send out the blood when. 
necessary. It is protected by a bag, called the per 
which is made of strong and rough materials. case 
holds a very little water—just enough to permit the heart to 
move easily and freely—and is placed between the lungs. 
The lungs fill all that cavity in the chest not occupied by the 
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