68 A MANUAL OF PHYSIOLOGY 



of the blood is divided into two portions, very distinct 

 from each other, both anatomically and functionally the 

 respiratory or lesser circulation, and the systemic or greater 

 circulation. Starting from the left ventricle, the blood passes, 

 along the systemic vessels arteries, capillaries, veins and, 

 on returning to the heart, is poured into the right auricle, 

 and thence into the right ventricle. From the latter it is 

 driven through the pulmonary artery to the lungs, passes 



FIG. 16. DIAGRAM OF THE GENERAL COURSE OF THE CIRCULATION. 

 RA, LA, right and left auricles ; RV, LV, right and left ventricles. 



through the capillaries of these organs, and returns through 

 the pulmonary veins to the left auricle and ventricle. The 

 portal system, which gathers up the blood from the in- 

 testines, forms a kind of loop on the systemic circulation. 

 The lymph-current is also in a sense a slow and stagnant 

 side-stream of the blood circulation ; for substances are con- 

 stantly passing from the bloodvessels into the lymph-spaces, 

 and returning, although after a comparatively long interval, 

 into the blood by the great lymphatic trunks. 



Physiological Anatomy of the Vascular System. The heart is 

 to be looked upon as a portion of a bloodvessel which has 



