224 



THE CIRCULATORY SYSTEM 



[CH. XIX. 



called lymph, is gathered up and carried back again into the blood by 

 a system of vessels called lymphatics. 



The principal vessels of the lymphatic system are, in structure, 

 like small thin-walled veins, provided with numerous valves. The 

 beaded appearance of the lymphatic vessels shown in figs. 208 and 

 209 is due to the presence of these valves. They commence in fine 

 microscopic lymph-capillaries, in the organs and tissues of the body, 



Lymphatics of head and 

 neck, right. 



Right internal jugular 



vein. 

 Right subclavian vein. 



Lymphatics of right arm. 



Receptaculum chyli. 



Lymphatics of lower ex- 

 tremities. 



Lymphatics of head and 

 neck, left. 



Thoracic duct. 



Left subclavian vein. 



Thoracic duct. 



Lacteals. 



Lymphatics of lower ex- 

 tremities. 



FIG. 207. Diagram of the principal groups of lymphatic vessels. (From Quaiu.) 



and they end in two trunks which open into the large veins near the 

 heart (fig. 207). The fluid which they contain, unlike the blood, 

 passes only in one direction, namely, from the fine branches to the 

 trunk, and so to the large veins, on entering which it is mingled with 

 the stream of blood. In fig. 207 the greater part of the contents of 

 the lymphatic system of vessels will be seen to pass through a com- 

 paratively large trunk called the thoracic duct, which finally empties 

 its contents into the blood-stream, at the junction of the internal 



