The Blood and its Circulation 145 



pulmonary veins carry arterial blood to the left auricle from 

 the lungs. 



From the left ventricle springs the largest arterial trunk 

 in the body, called the aorta. From the aorta other arteries 

 branch off to carry the blood to all parts of the body. 

 X 219, The Arteries. The blood vessels are tubes through 

 which the blood is carried to and from the tissues. There 

 are three kinds, the arteries, the veins, and the capillaries. 



The arteries are the highly elastic and extensible tubes 

 which carry the blood from the heart to all parts of the 

 body. All the arteries except the pulmonary may be 

 regarded as branches of the aorta. 



^ 220. The Aorta and its Great Branches. After the aorta 

 leaves the left ventricle it rises towards the neck, but soon 

 turns downwards, making a curve known as the arch of 

 the aorta. 



From the arch are given off the arteries which supply 

 the head and arms with blood. These are the two carotid 

 arteries, which run up on each side of the neck to the head, 

 and the two subclavian arteries, which pass beneath the 

 collar bone to the arms. 



The aorta now passes down in front of the spine to the 

 pelvis, giving off arteries to the different organs. Of these 

 branches the chief are the coaliac artery, which supplies the 

 stomach, the liver, and the spleen ; the renal arteries, one 

 to each kidney ; and the mesenteric arteries, which supply 

 the intestines. 



The aorta at last divides into two main branches, the 

 common iliac arteries, which, by their subdivisions, furnish 

 the arterial vessels for the pelvis and the lower limbs. 



221, The Veins. The veins are the blood vessels which 

 carry the impure blood from the various tissues of the body 

 to the heart. They begin in the minute capillaries and, 



