The Lymphatic System in Human Embryos. 



89 



The only structures with which the developing lymph nodes 

 could be confused are the sympathetic ganglia. On this account 

 care must be exercised, especially around the retroperitoneal sac, 

 where both structures are very abundant. The sections of these 

 stages are thick (50 to 100 microns) and the low powers of the 



Fig. 18. Transverse section through the abdominal cavity of a human 

 embryo, 80 mm. long, Mall collection, No. 172. It shows the kidneys, a 

 little of the liver, and many loops of the intestine, x about 8. A. m. s., 

 arteria mesenterica superior ; C. c, cisterna chyli at its lower border ; Lg. m., 

 lymphoglandulae mesentericae ; S. 1. m., saccus lymphaticus mesenterica. 



microscope are inadequate to distinguish them, especially when the 

 connective tissue around the ganglia is broken. With care and serial 

 sections the lymph nodes can be absolutely determined. 



The significance of this retroperitoneal sac is brought out in the 

 injected specimens in Dr. Heuer's paper. It will be noted that in 



