Chap. XI] 



THE VASCULAR SYSTEM 



187 



and gradually assume the characteristics of veins. The veins 

 unite to form the pulmonary veins. 



The pulmonary veins. — The pulmonary veins are four short 

 trunks which convey the oxidized blood from the lungs to the 

 left auricle, and which are found, tw^o on each side, — in the 



Entrance of 

 ,vena azygos 



Branch of pul- 

 monary artery 



Fig. 118. — Pulmonary Veins, seen in a Dorsal View of the Heart and 

 Lungs. The left lung is pulled to the left, and the right lung has been partly cut 

 away to show the ramifications of the air-tubes and blood-vessels. (Gerrish.) 



root of the corresponding lung. The pulmonary veins have no 

 valves. 



The general system. — This is the larger system and provides 

 for the circulation of blood from the left ventricle to all parts 

 of the body by means of the aorta and its branches, and the return 

 to the right auricle by means of the vense cavse. This is called the 

 systemic circulation. 



The blood-vessels of the general system. — The blood-vessels 

 of the general system consist of (1) the aorta, and all the arteries 

 that originate from it, (2) the capillaries which connect the 

 arteries and veins, and (3) all the veins of the body which empty 



