THE BLOODVESSELS. 51 



easily when wounded. On the contrary, the arteries when 

 cut across, remain open, and when wounded do not heal so per- 

 fectly ; in order to close, they must be obliterated, either by 

 pressure or by the use of the ligature. 



94. Arterial System. From a single artery called the 

 aorta, springing from the left ventricle of the heart, all the 

 arteries of the body arise. It must be borne in mind that the 

 artery called the pulmonary springs from the right ventricle, 

 and carries the venous blood to the lungs. The accompanying 

 figure (32) explains perfectly the course of this great artery 

 (the aorta), from its commencement in the heart, to its ter- 

 mination ; also of all the great branches which arise from it. 



95. Venous System. The veins originating in the 

 capillary vessels, in which the arteries terminate, follow 

 pretty nearly the course of the arteries ; but they are more 

 numerous and more superficial. 1 Many are situated imme- 

 diately beneath the skin, imbedded in the superficial fascia 

 of the body. Others follow the course of the arteries, to ter- 

 minate however at length in two large trunks, which empty 

 themselves into the right auricle of the heart (Fig. 30).* 



The veins of the intestines present this remarkable anomaly 

 that they unite into a single trunk, which, instead of joining 

 the venous system, directly proceeds towards the liver, and is 

 ramified through that organ after the manner of an artery ; 

 but the veins which leave the liver unite with the vena cava 

 inferior before that vessel enters the right auricle. 



96. Lesser Circulation. The venous blood conveyed 

 into the right auricle by the two cavae and by the coronary 

 vein, passes from this auricle into the right ventricle, and by 

 its action is driven along the pulmonaiy artery into the lungs 

 (Figs. 30 and 31). The latter vessel is called an artery, 

 although it carries only venous blood. In the right lung it 

 divides into three branches, and in the left into two ; thus cor- 

 responding as it were with the number of the lobes of each lung. 



97. The pulmonary veins, as they are called, carry back 

 from the lungs the whole of the blood which has been conveyed 

 to these organs by the pulmonary artery. In the capillary 

 system of these vessels, the blood has been in the mean 

 time aerated, revivified, and arterialized, and fitted once 

 more to perform its part in renovating the organs and 

 maintaining life. From the left auricle, in which the four 



* A smaller vein, called coronary, returns the blood which has circulated iu 

 the walls of the heart into the same cavity. R. K. 

 B2 



