%e Origin and Development of the Lymphatic System. 43 



iround the aorta are very abundant, so that the non-vascular 

 s small. Just opposite the adrenal anlage, however, there is a 

 ion zone which is less vascular. It marks the end of the azygos 

 Below this level the segmental veins drain through the Wolffian 

 and here the lymphatics form a wider plexus, which becomes 

 terna ehyli, fig. 10. As in the adult there is a gradual tran- 



13. — Section through the upper thoracic region of an embryo pig 

 ing 25 mm. in which the blood vessels are injected, to show the 

 of the right lymphatic duct approaching the heart. Magnified 40 

 The injection of the blood vessels was made through the umbilical 

 A. = aorta; D. C. = duct of Cuvier; D. t. = ductus thoracicus; E. 

 hagus; L. = lymph vessels to the heart from the right lymphatic 

 V. v. = nervus vagus; P. = pericardium; T. = trachea; V. a. = 

 ygos. 



between the cisterna chyli and the rest of the aortic plexus. 

 ie part which extends caudalward and the part which extends 

 lward. Figure 10 shows the cisterna chyli while it is still a 

 and not a sac. The series shows that in many places this dorsal 

 of lymphatics is sending sprouts around to the ventral prse- 

 sac. All of the abdominal sacs, the retroperitoneal, ventral to 

 ta, the two lateral iliac sacs and the dorsal plexus connect with 



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