ANGIOLOGY. 



rPHE vascular system is divided for descriptive purposes into (a) the blood 

 ; vascular system, which comprises the heart and bloodvessels for the circula- 

 tion of the blood; and (6) the lymph vascular system, consisting of lymph glands 

 and lymphatic vessels, through which a colorless fluid, the lymph, circulates. It 

 must be noted, however, that the two systems communicate with each other and 

 are intimately associated developmentally. 



The heart is the central organ of the blood vascular system, and consists of a 

 hollow muscle; by its contraction the blood is pumped to all parts of the body 

 through a complicated series of tubes, termed arteries. The arteries undergo 

 enormous ramification in their course throughout the body, and end in minute 

 vessels, called arterioles, w r hich in their turn open into a close-meshed network 

 of microscopic vessels, termed capillaries. After the blood has passed through the 

 capillaries it is collected into a series of larger vessels, called veins, by which it is 

 returned to the heart. The passage of the blood through the heart and blood- 

 vessels constitutes what is termed the circulation of the blood, of which the following 

 is an outline. 



The human heart is divided by septa into right and left halves, and each half 

 is further divided into two cavities, an upper termed the atrium and a lower the 

 ventricle. The heart therefore consists of four chambers, two, the right atrium 

 and right ventricle, forming the right half, and two, the left atrium and left ventricle 

 the left half. The right half of the heart contains venous or impure blood; the left, 

 arterial or pure blood. The atria are receiving chambers, and the ventricles dis- 

 tributing ones. From the cavity of the left ventricle the pure blood is carried into 

 a large artery, the aorta, through the numerous branches of which it is distributed 

 to all parts of the body, with the exception of the lungs. In its passage through 

 the capillaries of the body the blood gives up to the tissues the materials necessary 

 for their growth and nourishment, and at the same time receives from the tissues 

 the waste products resulting from their metabolism. In doing so it is changed 

 from arterial into venous blood, which is collected by the veins and through them 

 returned to the right atrium of the heart. From this cavity the impure blood 

 passes into the right ventricle, and is thence conveyed through the pulmonary 

 arteries to the lungs. In the capillaries of the lungs it again becomes arterialized, 

 and is then carried to the left atrium by the pulmonary veins. From the left atrium 

 it passes into the left ventricle, from which the cycle once more begins. 



The course of the blood from the left ventricle through the body generally to 

 the right side of the heart constitutes the greater or systemic circulation, while its 

 passage from the right ventricle through the lungs to the left side of the heart is 

 termed the lesser or pulmonary circulation. 



It is necessary, however, to state that the blood which circulates through the 

 spleen, pancreas, stomach, small intestine, and the greater part of the large intes- 

 tine is not returned directly from these organs to the heart, but is conveyed by the 

 portal vein to the liver. In the liver this vein divides, like an artery, and ultimately 

 ends in capillary-like vessels (sinusoids), from which the rootlets of a series of veins, 

 called the hepatic veins, arise; these carry the blood into the inferior vena cava, 

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