94 George Heuer. 



ecxceedingly important point, namely, that the lymphatic vessels 

 grow from the sacs, there are still differences. It was to test this 

 point that the present study was undertaken at the suggestion of 

 Dr. Sabin. I believe that this work, showing that the vessels of 

 the intestine grow from the retroperitoneal sac, strengthens her 

 position that the lymphatic system is derived from the sacs. Cer- 

 tainly the theory is a fruitful one, for injections of the retro- 

 peritoneal sac give the key for tracing the growth of the lymphatic 

 vessels to the viscera. 



The literature and general relations of the problem are given 

 by Dr. Sabin in the article on the development of the lymphatics- 

 in human embryos in this same journal and therefore only the 

 work on the retroperitoneal sac will be mentioned here. This sac 

 was discovered by F. T. Lewis^ who described it as a part of the 

 lymphatic system in 1906. 



It has been thoroughly worked out by Mr. W. Bsetjer,- in this 

 laboratory. 



Mr. Bastjer has shown that in pig embryos 17-19 mm. long there 

 are small branches of the large renal anastomosing vein in the root 

 of the mesentery. These small veins are ventral to the renal vein 

 and run in an antero-posterior direction. In embryos 19 and 20 

 ram. long these veins increase markedly in size and number, and 

 by the time the embryo is 21 mm. long show sac-like dilatations 

 which are still readily injected from the renal vein. From this 

 time on the sac formation goes on rapidly; in embryos 22-23 mm. 

 long, these small sacs have been completely transformed into a large 

 median sac entirely cut off from the veins and likewise independent 

 of the cisterna chyli. By the time the pig is 2.7 cm. long, this 

 sac is abundantly connected with the cisterna chyli, which forms 

 from the veins dorsal to the aorta, and an injection into the thoracic 

 duct will flow through the cisterna chyli into the retroperitoneal 

 sac. 



Methods and Material. This paper begins with the stage at 

 which Mr. Bsetjer left off, namely, where the retroperitoneal sac- 



'Lewis, Amer. Jour, of Anat, Vol. V.. 1906. 

 "Bsetjer, Amer. Jour, of Anat, Vol. VIII. 



