THE LYMPHATIC SYSTEM. 



:: 



E lymphatic system consists (1) of complex capillary networks which collect the 

 lymph in the various organs and tissues; (2) of an elaborate system of collecting 

 essels which conduct the lymph from the capillaries to the large veins of the neck 

 at the junction of the internal jugular and subclavian veins, where the lymph is 

 poured into the blood stream; and (3) lymph glands or nodes which are inter- 

 spaced in the pathways of the collecting vessels filtering the lymph as it passes 

 through them and contributing lymphocytes to it. The lymphatic capillaries and 

 collecting vessels are lined throughout by a continuous layer of endothelial cells, 

 forming thus a closed system. The lymphatic vessels of the small intestine receive 

 the special designation of lacteals or chyliferous vessels; they differ in no respect 

 from the lymphatic vessels generally excepting that during the process of digestion 

 thev contain a milk-white fluid, the chyle. 



Left innominate 



Jugular lymph-sac 

 Eight innominate 



Prerenal part of 

 inferior vena cava 



Postrenal part of 

 inferior vena cava 



Posterior lymph-sac 



Internal jugular 

 External jugular 



Duct of Cuvier 



Left cardinal 



Cisterna chtjli 

 Left renal 

 Retro-peritoneal 

 lymph-sac 



Left common iliac 

 External iliac 

 Hypogastric 



FIG. 592. Scheme showing relative positions of primary lymph sacs based on the description given by 



Florence Sabin. 



The Development of the Lymphatic Vessels. The lymphatic system begins as 

 a series of sacs 1 at the points of junction of certain of the embryonic veins. These 

 lymph-sacs are developed by the confluence of numerous venous capillaries, which 

 at first lose their connections with the venous system, but subsequently, on the 

 formation of the sacs, regain them. The lymphatic system is therefore develop- 

 mentally an offshoot of the venous system, and the lining walls of its vessels are 

 always endothelial. 



In the human embryo the lymph sacs from which the lymphatic vessels are 



1 Sabin, Am. Jour. Anat., 1909, vol. ix; Johns Hopkins Hospital Reports, 1913. 



(683) 



