THE LYMPHATIC SYSTEM 



773 



in number two paired, the jugular and the posterior lymph sacs; and two unpaired, the retro- 

 peritoneal and the cisterna chyli. In lower mammals an additional pair, subclavian, is present, 

 but in the human embryo these are merely extensions of the jugular sacs. 



The position of the sacs is as follows: (1) jut alar sac, at the junction of the subclavian vein 

 with the primitive jugular; (2) posterior sac, at the junction of the iliac vein with the post- 

 cardinal; (3) retroperitoneal, in the position of the cross branch between the renal veins; (4) 

 cisterna chyli, at the site of the cross-branch between the two iliac veins (Fig. 551). From the 

 lymph sacs the lymphatic vessels bud out along fixed lines corresponding more or less closely to 

 the course of the embryonic bloodvessels. They all arise as endothelial outgrowths, which later 

 become canalized. Both in the body wall and in the wall of the intestine the deeper plexuses are 

 the first to be developed; by continued growth of these the vessels in the superficial layers are 

 gradually formed. It is as yet undetermined whether the thoracic duct is formed from anas- 

 tomosing outgrowths from the jugular sac and cisterna chyli or whether it is developed by the 

 transformation of some of the radicles of the azygos veins. At its connection with the cisterna 

 chyli it is at first double, but the right vessel soon joins with the left. 



All the lymph sacs except the cisterna chyli are, at a later stage, divided up by slender con- 

 nective-tissue bridges and transformed into groups of lymph nodes. The lower portion of the 

 cisterna chyli is similarly converted, but its upper portion remains as the receptaculum chyli. 



Left innominate 



: 



Jugular lymph-sac J 

 Eight innominate' ~ 



Vena cava superior . 



F 're-renal part of 

 vena cava inferior. 



Post-renal part of 

 vena ca/va inferior 



Cisterna chyli 

 Posterior lymph-sac ~ 



Internal jugular 

 External jugular. 



Duct of Cuvier 



Left cardinal; 



Left capsular 

 Left renal 

 Metro-peritoneal 

 lymph-sac; 



& ; t Left common iliac 

 m- 'External iliac 

 Internal iliac 



FIG. 551. Scheme showing relative positions of primary lymphatic sacs based on the description given by 



Florence Sabin. 



Applied Anatomy. The lymphatic channels and nodes draining any infected area of the 

 body are very liable to become infected, and do so with the production of acute or chronic lymph- 

 iinijifis and lymphadenitis. In acute cases the paths of the superficial lymphatics are often 

 marked out on the skin by the appearance over them of the four cardinal signs of inflammation 

 pain, redness, heat, and swelling while the nodes swell and may suppurate. Chronic inflam- 

 mation leads to growth and fibrosis of the lymphatics and the connective tissue around them; 

 obstruction to the passage of the lymph results, as the fibrous tissue contracts and causes stenosis 

 or obliteration of the lymphatic channels, and hard edema of the involved skin and subcutaneous 

 tissue follows (pachydermia lymphanr/iectatica'). Chronic lymphangitis, together with the 

 blocking of numerous lymphatic vessels by the escaped ova of the minute parasitic worm Micro- 

 filaria nwturna, is the cause of elephantiasis, a condition common in the tropics and subtropics, 

 and characterized by enormous enlargement and thickening of the integument of some part of 

 the body, most frequently the leg. Tubercular and syphilitic enlargements of the lymphatics 

 and nodes are both very commonly met with. Primary tumors of the lymphatics are lymphan- 

 gioma and endothelioma; the so-called "congenital cystic hygroma" of the neck, arm, trunk, 

 or thigh is a cystic lymphangioma. Primary tumors of the lymph nodes may be benign (lymph- 

 adenoma, myxoma, ehondroma) or malignant (lymphosarcoma); cancer is an extremely common 

 secondarv affection. 





