FATE OF PRIMARY LYMPH-SACS IN ABDOMINAL REGION OF PIG, ETC. 27 



LYMPHATICS ARISING DORSO-LATERAL TO THE AORTA. 



Besides the paired anterior or jugular sacs there is another pair, the iliacs, 

 which grow along the dorso-medial edge of the Wolffian body, dorso-lateral to the 

 aorta, and drain the posterior half of the body. Figure 4 shows these two iliac sacs 

 slightly dorso-lateral to the aorta and also their relation to the cisterna chyli and 

 thoracic duct. It will be noted that there is an extensive plexus between the 

 two sacs, while the paler vessels in the depth are from the retroperitoneal sac. 

 The remnants of the Wolffian bodies show at the posterior borders of the kidneys. 

 The iliacs are connected with the jugulars by the cisterna chyli and thoracic duct. 

 Sabin (1912) has shown that the cisterna chyli and iliac sacs arise from the mesone- 

 phric veins of the vena cava. 



In the younger specimens, in the region of the diaphragm the thoracic duct is 

 seen as two vessels, one on either side of the aorta, lying dorsally. These anasto- 

 mose freely in front of and behind the aorta by lateral vessels. At about the same 

 level as the anterior end of the retroperitoneal sac the vessels of the thoracic duct 

 unite to form posteriorly an irregular dilatation, the cisterna chyli, extending to a 

 point near the posterior poles of the kidneys. 



From the lymphatics lying dorso-lateral to the whole length of the aorta that 

 is, from the thoracic ducts, the cisterna chyli and the anastomosing iliac sacs- 

 other lymphatics are given off dorsally as satellites of the segmental arteries which 

 accompany the anterior and posterior rami. No vessels were observed, however, 

 to enter the vertebral canal with the spinal branch of the posterior ramus, which is 

 in accord with previous embryological studies, from which it was evident that the 

 central nervous system contains no lymphatics. 



ILIAC SACS. 



Caudal to the cisterna chyli, and draining into it, are two large trunks, one on 

 either side of the aorta. These are the paired iliac sacs, which in earlier stages 

 appear to be united. Small at the cephalic end where they form the cisterna chyli, 

 they broaden out gradually to form a rectangular sac between the dorso-medial 

 surfaces of the kidneys and show two expansions. The lateral one is at the hilum 

 of the kidney to which it sends vessels and a small trunk extending laterally in the 

 body- wall to a retrorenal position, then turning abruptly caudad to unite with a 

 trunk from the posterior portion (fig. 2, Ramus retroren.). In older embryos the 

 latter gradually disappears. The other expansion occurs at the posterior end and 

 may be called the caudal portion of the iliac sac. It is roughly fan-shaped, the 

 expansion being latero-posterior, the outer margin curving with the posterior pole 

 of the kidney (fig. 4, S. II. pars caud.). 



In later stages, even at 5 cm., a distinct change is noted in the lymphatics dorso- 

 lateral to the aorta (fig. 4). The iliac sacs are no longer fused, but come to lie on 

 either side of the midline between the aorta and the medial edge of the kidney. 

 They empty through one or two trunks into the cisterna chyli in the region of the 

 adrenals. Their median border, accompanying the aorta, is straight and may 

 sometimes, even in the earlier stages, send anastomosing vessels to the other side. 





