ANATOMY OF THE HEART AND BLOOD-VESSELS. 223 



thigh. All the blood which leaves the heart by the aorta, 

 except that flowing through the coronary arteries, is finally 

 collected into the superior and inferior vence cavce (cs and ci, 

 Figs. 90 and 91), and poured into the right auricle. The 

 jugular veins which run down the neck, carrying back the 

 blood which went out along the carotid arteries, unite below 

 with the arm-vein (subdavian) to form on each side an in- 

 nominate vein (Asi and Ade, Fig. 90) and the innominates 

 unite to form the superior cava. The coronary-artery blood 

 after flowing through the capillaries of the. heart itself also 

 returns to this auricle by the coronary veins and sinus. 



The Pulmonary Circulation. Through this the blood 

 gets back to the left side of the heart and so into the aorta 

 again. The pulmonary artery, dividing into branches for 

 each lung, ends in the capillaries -of those organs'; From 

 these it is collected by the pulmonary veins, which carry it 

 back to the left auricle, whence it passes to the left ventricle 

 to recommence its flow through tho Body gencutlly. 



The Course of the Blood. From what has been said it is 

 clear that the movement of the blood is a circut"' Start- 



ing from any one chamber of the heart it will in time return 

 to it; but to clo this it must pass through at least two sets of 

 capillaries; one of these is connected with the aorta and the 

 other with the pulmonary artery, and in its circuit the blood 

 returns to the heart twice. Leaving the left side it returns to 

 the right, and leaving the right it returns to the left: and 

 there is no road for it from one side of the heart to the other 

 except through ;t <;upill;i.^ network. Moreover, it always 

 leaves fro; ricle through an artery, and returns to an 



auric! * \ein. 



Then- i - really only one circulation; but it is not un- 



common to &(.t'ak of two, the flow from the left side of the 

 heart to the right, through the Body generally, being called 

 the systemic, circulation, and from the right to the left, 

 through the lungs, the pulmonary circulation. But since 

 after completing either of these alone the blood is not back 

 at the point from which it started, but is separated from it by 

 the septum of the heart, neither is a "circulation" in the 

 proper sense of the word. 



Tho Portal Circulation. A certain portion of the blood 

 which leaves the left ventricle of the heart through the aorta 

 has to pass through three sets of capillaries before it can again 



