VESSELS CONNECTED WITH THE HEART. 199 



unite to form the superior and inferior vence caves or 

 the upper and lower hollow veins. These carry the blood 

 to the right auricle; thence it enters the right ventricle 

 from which arises one vessel, the pulmonary artery ; tin's 

 divides into a branch for each lung ; each branch splits up 

 into minute arteries in its own lung, and these end in the 

 pulmonary capillaries. From the pulmonary capillaries the 

 blood of each lung is collected into two pulmonary veins, 

 and the four pulmonary veins open into the left auricle. 



Summary. One artery, the aorta, arises from the left 

 ventricle. The blood carried out by the aorta comes back 

 by the upper and lower venas cavse to the right auricle; this 

 blood then goes to the right ventricle and is sent thence 

 through the pulmonary artery, which splits up into branches 

 for the lungs. The blood, carried out by the pulmonary 

 artery from the right ventricle of the heart, returns to the 

 left auricle by four pulmonary veins, two from each Jung ; 

 and then enters the left ventricle and begins its flow again 

 through the aorta. 



How the Heart is Nourished. The heart is a very hard- 

 worked organ, and needs an abundant supply of nourish- 

 ment. Its walls are much too thick to allow this to soak 

 in sufficient abundance all through them, from the blood 

 flowing through its cavities; accordingly they are perme- 

 ated by a very close network of capillary blood vessels. 

 These are supplied by the right and left coronary arteries 



Where do the venae cavse carry it? Where does it pass from the 

 right auricle? What vessel arises from the right ventricle? Into 

 what does the pulmonary artery divide? What happens to each 

 branch? How do the branches finally end? Into what is the blood 

 which flows through the pulmonary capillaries collected? Ho\v 

 many pulmonary veins are there? Where do they end? 



State briefly the course of the blood flow. 



