FATE OF PRIMARY LYMPH-SACS IN ABDOMINAL REGION OF PIG, ETC. 29 



difficult to analyze in terms of dorsal and ventral lymphatics. However, there are 

 glands arising from a small dorsal trunk or plexus which form the post-aortic or 

 prevertebral nodes, but these are few in number (fig. 5, Lymgl. praevert.). 



From the cephalic end of the iliac sacs lymphatics pass forward, anastomosing 

 with those from the retroperitoneal sac to supply the diaphragm (fig. 4, V. 1. diaph.). 

 The adrenals receive several vessels (V. 1. gl. suprar.) which arise from this cephalic 

 end of the sacs in company with those which pass to the diaphragm. As mentioned 

 previously, the kidney receives at its hilum vessels from the iliac sac (fig. 4, V. 1. ren.). 

 There appears, therefore, to be a double supply to that organ, the vessels from the 

 iliac sacs and those from the posterior half of the retroperitoneal sac. These vessels 

 do not seem to penetrate very deeply into the kidney. Besfdes the vessels to the 

 hilum of the kidney, a rather stout trunk, broad at the base, arises at this point and 

 extends laterally in the dorsal wall. At times this is quite a large lateral expansion 

 from the iliacs and forms a retrorenal sac which gives off one or more branches 

 passing posteriorly at right angles to the body-wall, and anastomosing with similar 

 vessels from the caudal end of the iliacs (fig. 2, Ramus retroren.) . It also sends a few 

 vessels into the lateral body-wall, where a small plexus is formed which drains part 

 of the deeper layers of the wall. Very few if any superficial vessels drain into it. 

 As stated before, in older embryos these retrorenal branches could not be injected. 



Caudal portion of sac. The fan-shaped caudal portion of each iliac sac lies in 

 the body-wall between the posterior pole of the kidney and the bifurcation of the 

 aorta (fig. 4) . It extends laterally and dips ventrally on its mesial side. Later it 

 forms an inverted Y-shaped expansion, one branch passing laterally along the 

 posterior pole of the kidney, the other going directly caudal and then turning 

 ventrally to supply the lower portion of the body and legs. 



From the lateral branch, in the earlier stages, a few vessels or a small trunk 

 course cephalad to anastomose with the vessels from the retroperitoneal sac. 

 Laterally, this caudal portion sends a group of lymphatics through the body-wall 

 to form a superficial node just above the crest of the ilium (the ilio-inguinal node) 

 which is characteristic for the pig, and drains the skin of the posterior half of the 

 body and tail (Sabin, 1904). From the medial side of the posterior branch of the 

 caudal portion one or two vessels pass caudally in the dorsal wall along with the 

 lateral sacral vein (fig. 4, V. 1. sacr. lat.). On the postero-medial side of the sac a 

 short trunk extends ventrally, medial to the umbilical artery, to anastomose with 

 another trunk from the retroperitoneal sac. 



The posterior trunk (fig. 4, T. post.), which drains the lymphatics of the legs 

 and some of the pelvic organs, is the continuation of the medial branch of the caudal 

 portion, which courses ventrally and laterally, passing lateral to the umbilical 

 artery along the common iliac artery (fig. 1 , T. il. com.) . Only the proximal portion 

 of the posterior trunk is shown in figure 4, for as it turned ventrally it became less 

 and less distinct from the dorsal side of the embryo; but in figure 1, which is a 

 ventral view of the same specimen, the continuation of the posterior trunk is well 

 seen. It divides into several branches, two of which are proximal. From its medial 

 edge, near its origin, the trunk sends a vessel ventro-medially to the lateral side of 



