BLOOD SYSTEM. 



413 



the junction of the right subclavian and right jugular 

 veins. The former (left thoracic duct) drains the whole 

 of the viscera, the whole of the lower limbs and the left 

 side of the trunk, the left arm, and the left side of the 

 head, while the latter (right thoracic) drains only the right 

 side of the trunk, the right arm, and right side of the 

 head. Fig. 291 is a diagram showing this. 



Structure. — The valvular structure is everywhere 

 conspicuous, and gives a beaded appearance to these 

 vessels. The valves open toward the 

 main trunks, and therefore toward the 

 heart, and tend to prevent backward 

 movement. This is the more neces- 

 sary as there is no impelling heart, the 

 force of motion being only a suction 

 force at the extremities. Doubtless 

 movements of the body and pressure 

 of the muscles tend to force on the con- 

 tained fluid (Fig. 292). 



Function. — Their function seems 

 to be: 1. The absorptio7i of waste. 2. The 

 absorption of excess of plasma exuded 

 from the capillaries into the tissues. 

 These two are going on everywhere and 

 at all times. 3. In the case of those of 

 the intestines (lacteals), in addition to 

 these two and at particular times, also 

 the absorption of the digested food. In 

 all these functions they are assisted 

 by the capillary blood vessels. 



Lymphatic Glands. — In the 

 course of the lymphatic vessels everywhere, but espe- 

 cially the bend of the joints, as in the bend of the elbow 

 and knee, in armpit and groin, and in the spaces be- 

 tween the swelling muscles, as on the side of the neck, 



Fig. 292. — Enlarged 

 section of a lym- 

 phatic vessel, show- 

 ing valves, v. 



