Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 352 HUMAN PHYSIOLOGY membranous bag called the pericardium. The inner lining of the pericardium secretes a fluid in which the heart lies. This fluid prevents any friction which otherwise might arise from the con- stant movement of the heart against the surrounding tissues. When, for any reason, the pericardial fluid is not secreted; inflam- mation arises in that region. Internal Structure of Heart. — If we should cut open the hea
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 352 HUMAN PHYSIOLOGY membranous bag called the pericardium. The inner lining of the pericardium secretes a fluid in which the heart lies. This fluid prevents any friction which otherwise might arise from the con- stant movement of the heart against the surrounding tissues. When, for any reason, the pericardial fluid is not secreted; inflam- mation arises in that region. Internal Structure of Heart. — If we should cut open the heart of an ox, down the midline, we could divide it into two parts, each of which would have no internal connec- tion with the other. Each side of the heart is found to be distinct and to be made up of a thin-walled portion with a rather large internal cavity, the auricle, and a smaller portion with heavy mus- cular walls, the ventricle. The auricles occupy the base of the cone-shaped heart; the ventricles, the apex. The auricle of the right side communicates with the ven- tricle of that side. In the same manner the auricle of the left side is connected with the ventricle on the left side. Com- munication between auricles and ventri- cles is guarded by little flaps of muscle called valves. The auricles receive blood from the veins. The ventricles pump the blood into the arteries. From each ven- tricle, large arteries leave the heart; that of the left side is called the aorta. Through the aorta, blood passes to all parts of the body. On the right side, the pulmonary artery carries blood to the lungs. The openings to these arteries are guarded by three halfmoon-shaped flaps, which open so as to allow blood to pass away from the ventricle, but not to go back into it when the muscles relax. The heart is constructed on the same plan as a pump, the valves preventing the reflux of blood into the auricle after it is forced out of the ventricle.
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