n 



THE LYMPHATIC SYSTEM 



85 



connected with larger vessels of only one kind. 



That is to say they open only into trunks which carry 



fluid away from them, and thus bear the same relationship to 



the lymph-capillaries that the veins do to blood-capillaries. 



These trunks are known as the lymphatic vessels, 



and further resemble the small veins 



in the general structure of their walls 



and in being abundantly provided 



with valves, similar to those in the 



veins, which freely allow of the passage 



of lymph from the lymph-capillaries, 



but obstruct the flow of any liquid in 



the opposite direction. But the Ij'm- 



phatic vessels difi'er from the veins in 



that they do not rapidly unite into 



larger and larger trunks which present 



a continually increasing calibre and 



allow a flow without interruption to 



the heart. On the contrary, remaining 



nearly of the same size, they at intervals 



become connected with small rounded 



or often bean-shaped bodies, called 



lymphatic glands, entering the 



glands at one side and emerging at 



the opposite side as new lymphatic 



vessels (Fig. 26, </.). 



Sooner or later the great majority of 

 the smaller lymphatic vessels pour their 

 contents into a tube which is about as 

 large as a goose-quill, lies in front of 

 the backbone, and is called the thor- 

 acic duct. This opens at the root 

 of the neck into the conjoined trunks 

 of the great veins (jugular and sub- 

 clavian) which bring back the blood from the left side 

 of the head and the left ai-m. (Fig. 27, f.g.) 



The remaining lymphatics, chiefly those of the right 



Fig. 26.— The Lym- 

 phatics OK THE 

 Front of the 

 Right Arm. 



g, lymphatic glands, 

 on the course of 

 the lymphatics. 



