56 ELEMENTARY PHYSIOLOGY. 



right ventricle. The left auricle (V) forms the 

 upper chamber, and the left ventricle (X) the lower 

 chamber of the left side of the heart. The upper 

 and lower chambers that is, the auricles and ventri- 

 cles are separated by valves, whose important use 

 we will learn when we trace the course of the blood 

 through the heart. 



The arteries are the vessels which 



The Arteries. ,, , -, n . .. /. 



carry the blood in its course from 

 the heart. All the arteries which distribute bright 

 or pure blood from the heart for the nourishment of 

 the body, are represented by red vessels on the plate. 

 This large artery the pulmonary artery (16) 

 carries dark or impure blood ; so it is shown in blue. 

 Of course the arteries near the heart are very much 

 larger blood-channels than those farther out, where 

 they divide as you see, into very many branches. 



The veins are the vessels which gather 

 up the blood from all parts of the body 

 and carry it to the heart. All the veins which bring 

 dark, impure blood to the heart are represented by 

 blue vessels in the figure. This (31) large vein 

 the pulmonary vein carries pure blood; so it is 

 shown in red. The veins near the heart are very 

 much larger than those which are farther away. 

 There are valves in the veins to prevent the blood 

 from flowing or setting back in a wrong direction. 



The capillaries are very fine tubes 



The Capillaries. .. . ..* ,, 



connecting the arteries with the 



