16 /.'. Sabin. 



tion happens t" be cut in the right plane foi each valve. For 

 the jugular sac frontal sections are the h -. 192, 194, Sabin 134). 



A ik'u . iii the Mall collection, No. 160, measuring '.'1 



in connection with the renal lymphatics. A care- 

 ful ruction of this specimen with abundant illustrations would 

 In' of value, but for the present 1 ran give only a description. I in- 

 jected the embryo with India ink into the umbilical artery while the 

 heart was >iill beating. The vascular injection i< almost perfect. The 

 embryo was then put directly into bichloride-acetic and the fixation 

 ccellent. 



In marked contrast in the embryo pig of about the same length. 

 Wolffian bodies are disappearing, being pushed caudalward by the 

 iving permanent kidneys. The cerebral pole of the Wolffian bodies 



• far to the side opposite the median mesonephritic Vein which, as 

 Baetjer (8, fig. '. i shows, connects tli<' Wolffian h<>die< opposite their 

 lii I ii i n in embryo pigs measuring 20 nun. This median vein in the 

 human embryo (No. 160) passes over the ventral surface of the adrenal 

 bodies and -till receives the veins of the cerebral pole of the Wolffian 

 bodies. Ii also ; a plexus of veins from the permanenl kidneys. 



It i- markedly asymmetrical mi account of the development of the 

 vena cava on the right side. 



B lod-filled lymphatic buds completely surround this mesonephritic 

 vein in the midline, making the anlage of the retroperitoneal or 

 prae-aortic sa< ; some of those that come from the dorsal surface of the 

 \ein have pushed between the ma>se> of the sympathetic ganglia ami 

 reached "the dorsal surface of the aorta. In some sections, the retro- 

 peritoneal buds are partly emptied id' their blood. The area at the 

 root <<( the mesentery opposite the median mesonephritic vein i- small 

 in the human embryo as compared with the corresponding area in I 

 pig and the retroperitoneal sac is correspondingly small. 



The iliac sacs and the beginning thoracic dint are also present. 

 Uong the dorso-medial wall of the kidney in the angle between the 

 mental veins and the plexus of renal veins are two long iliac sacs. 

 'I'h.', are evidently farther advanced than the retroperitoneal sac, for 

 they are nearly empty. The one on the left side measures I 8 mm. 

 ami extend- t < » the bifurcation of the aorta. On the right side the 

 empty Bac i- considerably Bhorter, hut it- lower part i- replaced by 

 blood-filled buds along the inferior vena cava. 



