The Origin and Development of the Lymphatic System. 31 



iliac lymphatics. For the present I shall describe the renal lymphatics 

 from sections which can be done in the blood-packed stage. 



The description of the iliac lymphatics, however, needs an outline 

 of the blood vessels of the region. If the veins of the prevertebral 

 space between the level of the median vein connecting the Wolffian 

 bodies and the root of the tail be injected it will prove that they 



Fig. 9. — Section through the hilus of the Wolffian bodies to show the place 

 of origin of the iliac lymphatic vessels and the abdominal part of the 

 thoracic duct in an embryo pig 23 mm. long. (Specimen 23b.) Magnified 

 50 times. A. = aorta; G. s. s. c. = gl. suprarenalis s. corticalis; L. v. = 

 lymph vessels filled with blood; M. v. — vena mesonephritica; R. s. = retro- 

 peritoneal lymph sac, a part of which is filled with blood, a part empty; 

 W. b. = edge of the Wolffian body. 



are enormously abundant. In the embryo measuring 20 mm. the 

 segmental veins draining the cord and the body wall make an 

 extensive network, which drains in part into the median vein of the 

 Wolffian body and thence directly to the vena cava, while farther 

 caudalward this same plexus drains directly into the large surface 



