THE LYMPHATIC SYSTEM 



279 



renal bodies, and the cisterna chyli also appears, Paired posterior sacs 

 arise in relation to the sciatic veins in embryos 24 mm. long. These sacs 

 at first contain blood which they soon discharge into neighboring veins, 

 thereupon losing their venous connections. With relation to the lymph 

 sacs as centers, the thoracic duct (at 30 mm.) and the peripheral lymphatics 



FIG. 287. Flat reconstruction of the primitive lymphatic system in a human embryo 30 

 mm. long (Sabin). X about 3.5. C.c., Cisterna chyli; Lg., lymph gland; S.l.jug., jugular 

 lymph sac; S.l.mes., retroperitoneal lymph sac; S.l.p., posterior lymph sac; S.l.s., subclavian 

 lymph sac; V.c., cephalic vein; V.c.i., inferior vena cava; V.f., femoral vein; V.j.t., internal 

 jugular vein; V.I. p., deep lymphatics; V.l.s., superficial lymphatics; V.r., renal vein; V.s. t 

 sciatic vein; V.u.(p.) primitive ulnar vein. 



develop. The jugular- sacs alone acquire with, the internal jugular veins 

 secondary connections that are late^r utilized by the thoracic and right 

 lymphatic ducts. The various sacs themselves are eventually transformed 

 into chains of lymph nodes. 



Two discordant views exist as to the exact mode of origin and growth 

 of the lymphatics. According to Sabin (1909; 1916) and Lewis (1906), 



