CHAPTER IX. 



Circulation. Organs of the circulation; heart, pericardium; arteries, 

 capillaries, principal arteries; veins, principal veins ; portal system; 

 lymphatic vessels and ganglia. Mechanism of the circulation; dis- 

 coz'ery of the circulation, action and sounds of the heart, arterial circu- 

 lation, pulse, capillary circulation; venous circulation, valves of the 

 veins; discharge of chyle and lymph into the veins. Sanguification; 

 circulation in the pulmonary artery, capillaries, and pulmonary veins. 

 Influences which accelerate or retard the beating of the heart. 



Circulation. The blood is carried by the arteries from the 

 heart to all the organs, and it returns by the veins from all 

 the organs to the heart. This movement of the blood to and 

 from every portion of tire body, from the heart as the point 

 of departure, is called the circulation. The transportation of 

 chyle and lymph by the lymphatic vessels, which are the 

 tributaries and purveyors of the sanguiferous system, is con- 

 nected also with the circulation. 



Organs of the circulation. The heart is a hollow muscular 

 organ, nearly in the form of a cone, of which the base is 

 equal to the height, and about the size of the fist in the 

 adult. It is situated towards the middle of the chest, a little 

 to the left (fig. 24, p. 91), and between the pleurae, which 

 contribute to form its covering. Its apex is directed down- 

 ward, forward, and towards the left, at about the level of the 

 fifth rib; its base looks upward, and slightly backward, and 

 is protected by the sternum. Its anterior face, turned 

 upward and to the right, is marked by a longitudinal furrow, 

 as is also its posterior face, which is turned downward and to 

 the left. Internally the heart is divided by a muscular par- 

 tition into two nearly equal halves, placed back to back, and 



