180 THE CIRCULATORY APPARATUS 



valves. Columnce carnece are found in the right 

 ventricle, and the musculi papillares are very large; 

 one is attached to the anterior wall, the other to the 

 posterior. 



See Fig. 71 for relation of the valves and orifices of 

 the heart to the chest wall. 



The muscle fibers of the heart are attached to car- 

 tilaginous rings which surround the auriculoventricular 

 and arterial orifices. 



Nerves. (See pages 121, 383.) 



THE CIRCULATION OF THE BLOOD 



The heart is the pump which propels the blood, 

 aided by the elasticity of the arteries, veins, and 

 connecting capillaries throughout the body. Without 

 the rhythmical contraction of the heart muscle, life 

 cannot be maintained. The blood courses through 

 the cavities of the heart as follows. Allowing that 

 the heart has emptied its chambers, this blood is 

 returned to the heart as venous blood through the 

 superior and inferior vena cavse which open into the 

 right auricle, from which it passes to the right ven- 

 tricle through the auriculoventricular opening. The 

 blood now is forced into the pulmonary artery and 

 its branches to the pulmonary capillaries in the lungs, 

 where the blood, coming in contact with the air we 

 breathe, by a process of gaseous exchange, gives up 

 the carbon dioxide to the lungs, and absorbs oxygen, 

 becoming bluish red or scarlet in color. This new or 

 arterialized blood is carried back by the pulmonary 

 veins to the left auricle of the heart, flows through the 

 left auriculoventricular opening into the left ventricle 

 and thence through the aorta to the small arteries 

 coursing along until the capillaries are reached in 

 every part of the body, when by the same gaseous 

 exchange as we said occurred in the lungs, the blood 

 gives up its oxygen to the tissues and absorbs the 



