Elementary anatomy, physiology and hygiene for higher grammar grades . thevalve closes, and the blood cannot get back into the auri-cle, but it can pass out into the aorta, and from the aorta,which is the largest artery of the body, the blood is dis-tributed all over the body,coming back to the heartfrom the veins, and enter-ing the right the right auricle itcan pass through the tri-cuspid valve into the rightventricle, and when thisventricle contracts, thecusps of the tricuspidvalve are forced togetherand closed, while the valveinto the pulmonary arteryis forced open. The impure
Elementary anatomy, physiology and hygiene for higher grammar grades . thevalve closes, and the blood cannot get back into the auri-cle, but it can pass out into the aorta, and from the aorta,which is the largest artery of the body, the blood is dis-tributed all over the body,coming back to the heartfrom the veins, and enter-ing the right the right auricle itcan pass through the tri-cuspid valve into the rightventricle, and when thisventricle contracts, thecusps of the tricuspidvalve are forced togetherand closed, while the valveinto the pulmonary arteryis forced open. The impure blood passesout to the lungs to be puri-fied, and after purificationit returns through the pulmonary veins already referredto into the left auricle. The left side of the heart has to force the blood all overthe system, while the right side of the heart has only toforce the blood into the lungs which lie all about theheart in the thorax. For this reason the left side of theheart has a very heavy muscular wall, while the rightside of the heart has a much thinner Fig. 30. — Diagram illustrating the courseof the blood through the heart. [Tracy.] 136 PHYSIOLOGY 5. THE OKGANS WHICH CAUSE THE BLOOD TOCIRCULATE (continuled) THE AETBEIBS The tubes which conduct the water from the pump-ing system of the city to the various houses are composedof either stoneware or iron. The smaller subdivisionswithin the house which go to the different faucets aremetal. The system of tubes which conduct the blood over thebody begins at the heart with a large, thick-walled tube,a little larger than ones thumb. This tube is called theaorta. All of the tubes which carry blood away from the heartare called arteries. The aorta is the main trunk of thissystem of tubes. The accompanying plate (page 137)shows the aorta passing upward from the base of theheart, curving around at the base of the neck, and thenpassing downward along the spinal column. Notice thatit gives off branches as it passes downward a
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