CHAPTER VI 



THE CIRCULATORY SYSTEM 



THE ORGANS OF CIRCULATION 



The organs concerned with the circulation of blood and lymph 

 are the heart, the arteries, the veins, the capillaries, and the 

 lymphatics. 



Pulmonary I'eins 



Right branch of 



pulmonary 



artery 



Vena azygos 



Great coronary vein- 



Small coronary vei 



. Right coronary artery 



Fig. 39. — Right view of heart. The pericardium, epicardium, and subepicardial 

 fat have been removed. Cardiac vessels are injected. (Sisson, Anatomy of 

 Domestic Animals.) 



The heart is the central organ of this system (Figs. 39, 40) . 

 It is composed of muscle tissue and is situated in the thorax, 

 between the lungs and opposite the third to sixth ribs. It is 

 attached at the base to the large blood-vessels. It rests on noth- 

 ing, the apex being clear of the sternum. The average weight 



126 . 



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