Anatomy, physiology and hygiene for high schools . e up of cells whichdischarge a serumlikeor wheylike substance).These free surfaces ofthe two parts of tlie peri-cardium, the part liningthe heart and the partforming the sac, movefreely upon each otherwith the movements ofthe heart. The cavitybetween them containsa little fluid secreted bythe cells of the serousmembrane. The heart is conical inshape, the broad end, orbase,uppermost, the coneend, or apex, below. Theapex lies opposite thepoint of the chest wallat which we can feel theheart beat most strongly,between the fifth and sixth ribs to t
Anatomy, physiology and hygiene for high schools . e up of cells whichdischarge a serumlikeor wheylike substance).These free surfaces ofthe two parts of tlie peri-cardium, the part liningthe heart and the partforming the sac, movefreely upon each otherwith the movements ofthe heart. The cavitybetween them containsa little fluid secreted bythe cells of the serousmembrane. The heart is conical inshape, the broad end, orbase,uppermost, the coneend, or apex, below. Theapex lies opposite thepoint of the chest wallat which we can feel theheart beat most strongly,between the fifth and sixth ribs to the left of the the base of the heart the large arteries run out. Here atthe base on each side is a flat, soft, earlike structure connectedwith the firmer part below. These flabby structures are theappendages of the auricles (Latin auris, ear) of the firmer parts below inclose the ventricles (Latin venter,belly). The heart consists of four chambers—two auricles, rightand left, and two ventricles, right and left. At the base,. Heart aud lungs in chest. a, arteiies and veins to head (right); ft, arteries,veins, and nerves to ai-m (left); h, heart; I, Inng(drawn hack); p, pericardium. 156 PHYSIOLOGY AND HYGIENE posteriorly and to the left, lies the left auricle. In the com-paratively thin walls of this cavity are four small openings, the apertures of the pulmonaryveins,which bring- the blood fromthe lungs. In the lower wall ofthe auricle is a large openingto the left ventricle. The left rent ride lies in thelower part of the heart, to thefront and left. The walls of thiscavity are very thick and its upper wall is the open-ing from the left auricle. Thisopening is covered by a valvemade up of two flaps, the bicus-pid or mifraJ (Greek niifra, head-•Iress ) valve. The bases of thesevalve flaps are fixed about theauric ulo-ventricular edges are held by connec-tive tissue cords connecting withthe ventricular walls, the cJwrdcetendinece (G
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