LYMPH 



105 



from (he tissue or organ. The walls of a lymphatic vessel 



arc very delicate and thin, and are formed of a single layer of 



flattened cells joined edge to edge, the larger ones having in 



addition a little fine connective tissue and some 



plain muscular fibres outside this, but the walls 



arc nevertheless transparent. The lymphatic 



vessels of one organ or tissue join those of 



others; thus the lymphatic vessels of the leg 



are formed by the union of those from the 



muscles and other tissues of the limb. These 



vessels can be traced up the limb into the 



abdomen to a main lymphatic vessel lying in 



the trunk just in front of the vertebra?. This 



vessel is called the thoracic duct. It lies in 



the thorax on the front of the dorsal vertebra?, 



passes through the diaphragm, and extends 



down the abdomen to the level of the lumbar 



vertebra 1 , where the lymphatics from the legs 



and lower part of the trunk open into it. The 



lymphatics from the intestine and the other 



abdominal organs also open into it, so that the 



lower end of the thoracic duct is larger than the 



rest of it, and is called the receptaculum 



chyli. As the thoracic duct passes up the 



thorax the lymphatic vessels from tlie thoracic 



organs join it, and higher still it receives those FIG. 49. The lym- 



from the left ami and from the left side of the pltic vessels of the 



head and neck. The upper end of the thor- front f .' 



.... ..... arm. f, lymphatic 



acic duct, which is only a quarter of an inch in R i an ds. 

 diameter, turns towards the left side, and at 

 the root of the neck opens into the large vein the jugular 

 vein coming down the left side of the neck just as the vein 

 joins with the left subclavian vein, the main vein of the left 

 arm. The vein formed by the union of these two veins opens 

 into the superior vena cava. The lymphatics of the right arm 

 and right side of the neck are collected into a small duct which 

 opens into the right jugular vein. Thus the lymph, which 

 < -xiult-s from the blood capillaries, is returned by the lymphatic 

 vessels and the thoi.u ic duct to the blood again. 



Along the lymphatic \esscK and the thoracic duct are 



