40 ELEMENTARY PHYSIOLOGY less. 



the great veins of the body, are connected with opposite 

 sides of the heart ; and the great arteiy of the hnigs and 

 the great veins of the lungs also with opposite sides of 

 that organ. (Jn the other hand, the veins of the body 

 open into the same side of tlie heart as the artery of the 

 lungs, and the veins of the lungs (jpen into the same side 

 of the heart as the artery of the body. 



The arteries which open into the capillaries of the sub- 

 stance of the heart are called coronary arteries, and 

 arise, like the other arteries, from the aoita, but quite 

 close to its origin, just beyond the semilunar valves. But 

 the coronary vein, which is formed by the union of the 

 'small veins which arise from the capillaries of the heart, 

 does not open into either of the ven{« cavte, but pours the 

 blood which it contains directly into the division of the 

 heart into which these ven;c cavie open — that is to say, 

 into the right upper division (Fig. 19, h). 



The abdominal viscera referred to above, the veins of 

 which do not take the usual course, are the stomach, the 

 intestines, the spleen, and the pancreas. These veins all 

 combine into a single trunk, which is termed the portal 

 vein (Fig. 11, V.P.), but this trunk does not open into 

 the inferior vena cava. On the contrarj', having reached 

 the liver, it enters the substance of that organ, and breaks 

 up into an immense multitude of capillaries, which ramify 

 through the liver, and become connected with those into 

 which the artery of the liver, called the hepatic artery 

 (Fig. 11, H.A.), branches. From this comnion capillary 

 mesli-work veins arise, and iniite, at length, into a single 

 trunk, the hepatic vein (Fig. 11, H. V.), which emerges 

 from the liver, and opens into the inferior vena cava. 

 The flow of blood from the abdominal viscera through the 

 liver to the hepatic vein is called the portal circulation. 

 The portal vein is the only great vein in the body which 

 branches out and becomes continuous with the capillaries 

 of an organ, like an artery. But certain small veins in 

 the kidney are similarly arranged. (Lesson V.) 



