162 



CIRCULATION OF THE BLOOD 



from there again into the aorta. Thence it flows through all branches of 

 the aorta to the capillaries, from there to the systemic veins and through the 

 vence cavce back to the right auricle. That portion of the circulation from 



the left ventricle to the right auricle is called 

 the greater circulation. 



In warm-blooded animals the entire quantity 

 of the blood must flow through the lungs in order 

 to pass from the right half of the heart to the 

 left. During a complete circuit therefore the 

 blood flows through two systems of capillaries: 

 namely, (1) that of the greater circulation, and 

 (2) the pulmonary system. For the blood which 

 passes through the capillaries of the stomach, 

 intestine, pancreas and spleen still another capil- 

 lary system is interpolated. This blood flows to 

 the liver in the portal vein which there breaks 

 up into a new system of capillaries, whence arise 

 the hepatic veins, conducting the blood away to 

 the heart. The same is true of the kidney blood, 

 for in the kidneys themselves the blood flows first 

 through the capillaries which form the glomeruli 

 of the Malpighian corpuscles, and secondly 

 through the capillary plexus by which the kidney 

 tubules are surrounded. 



The contraction of the heart is designated the 

 systole and its relaxation, the diastole. 



FIG. 50. Schema of the cir- 

 culation, seen from the dor- 

 sal side, a, left auricle; 6, 

 left ventricle; c, right auri- 

 cle; d, right ventricle; e, 

 pulmonary circulation ; /, 

 capillaries of the intestine; 

 g, capillaries of the liver; h, 

 capillaries of the lower ex- 

 tremity; i, capillaries of the 

 head and upper extremities; 

 k, hepatic artery. Arterial 

 blood, red; venous blood, 

 blue; lymph vessels shown 

 only in outline. 



SECOND SECTION 



THE MOVEMENTS OF THE HEART 



1. THE FORM CHANGES OF THE 

 HEART IN SYSTOLE 



After opening the pericardium of a beating 

 heart it can be seen that the contraction begins 

 at the outlet of the great veins, which are here 

 surrounded by circular muscle fibers, and pro- 

 ceeds thence onto the auricles. 



The two auricles contract simultaneously, and 

 immediately after the auricular systole the ventricles contract, likewise 

 simultaneously. Neither auricles nor ventricles completely empty themselves 

 by their contractions. 



A. STRUCTURE OF THE VENTRICULAR WALL 



The arrangement of the muscular mass which forms the walls of the ven- 

 tricles is very complicated. Our description here must be very brief. 



Of the two ventricles the left, possesses a much stronger musculature than 



