38 Florence B. Sabin. 



veins of the Wolffian body. Opposite the lower pole of the Wolffian 

 body this plexus is ■ directly continued into the iliac veins. Cross 

 sections of injected embryos at this stage, namely, 20 mm., show that 

 the entire area lateral to the aorta and between the two Wolffian bodies 

 is practically filled with a plexus of these segmental veins. By the 

 time the embryo is 22 or 23 mm. long, however, there is a small non- 

 vascular area along the dorsal-medial edge of the Wolffian bodies, and 

 into this small area the iliac lymphatics bud. The earliest specimen 

 in which I have found these blood-filled buds measures 22 mm.; the 

 specimen is of interest because it shows clearly that the buds lie against 

 the veins of the Wolffian body itself as well as the median mesone- 

 phritie vein. The place of origin of the cisterna chyli and iliac' lym- 

 phatics can be best seen in fig. 9, which is a cross section of an embryo 

 measuring 23 mm. through the median mesonephritic vein. Just 

 lateral to the aorta are the masses of the sympathetic nervous system 

 through which runs the great plexus of the segmental veins, and the 

 cortex of the adrenal bodies. Ventral to the aorta is the mesonephritic 

 vein, and the retroperitoneal sac, some of the buds of which are full 

 of blood and some now partly empty. In the dorso-medial edge of the 

 two Wolffian bodies is the plexus of blood-packed lymphatic buds which 

 arches across the midline, and, as shown in fig. 10, which is farther 

 cerebralward, forms a definite blood-filled cisterna chyli in the midline. 

 My various series of cross sections of pigs of about the same meas- 

 urement are interesting, because they show the progression of the 

 buds. In a specimen (23a) the iliac lymphatics extend only as far as 

 the hilum of the permanent kidney which lies dorsal to the lower 

 pole of the Wolffian bodies. The iliac buds lie throughout their 

 course in the same relative position to the Wolffian bodies and the aorta 

 as is shown in fig. 9. In this specimen (23a) the iliac lymphatic 

 plexus is spreading over the capsule of the permanent kidney, showing 

 that it receives lymphatics while they are in the blood-filled stage. 

 In later stages I have injected lymphatics from the iliac sac around 

 the pelvis of the kidney. It is thus clear why the lymphatics of the 

 kidney drain into the iliac lymph glands, while those of the repro- 

 ductive glands which develop ventral to the Wolffian body drain 

 into the prse-aortic glands. In a series 23b from the same litter as 23a 

 the iliac plexus is complete, extending from the mesonephritic vein to 

 a dilated sac opposite the bifurcation of the aorta. It was this swollen 

 end of the iliac lymphatics that I identified in embryos 25 mm. long 



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