CHAPTER IX. 



THE VASCULAR SYSTEM. 



The vascular system is composed of the heart, ar- 

 teries, veins and capillaries. The heart is a muscular 

 organ, lined by an endocardium, which is the continua- 

 tion of the tunica intima of the blood vessels. Next 

 to the endocardium is the myocardium from within 

 out. The myocardium is the heart muscle. The outer 

 surface of the heart is covered by the pericardium: 

 this is a serous membrane, of white fibrous tissue, and 

 covered by endothelial cells. Numerous ganglia are 

 found in the tissues of the heart, along the course of 

 the nerves. The nerve supply of the heart is derived 

 from the pneumogastric and sympathetic system. The 

 fibers running from these centers are both medullated 

 and non-medullated. The first is from the pneumo- 

 gastric, and the second is from the sympathetic sys- 

 tem. The valves of the heart are simply broad folds 

 of the endocardium, between* which are a small amount 



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