FATE OF PRIMARY LYMPH-SACS IN ABDOMINAL REGION OF PIG, ETC. 37 



SUMMARY. 



In the posterior half of the body, the first stage in the formation of a connected, 

 well-developed primary lymphatic system in the pig is the presence of primary 

 lymph-sacs, lying ventral and dorsal to the aorta. The ventral sac is the large 

 retroperitoneal sac, which extends from the region of the cceliac axis to the bifurca- 

 tion of the aorta. Dorsal, or dorso-lateral, to the aorta is the remainder of the 

 primary system the paired iliac sacs which extend from the region of the adrenals 

 to the bifurcation of the aorta. 



According to their origin from these primary sacs, lymphatic vessels t>f the 

 organs and structures in the abdominal and pelvic regions fall into two great 

 groups, dependent upon whether they arise from the primary lymphatics ventral 

 to the aorta, or from the primary lymphatics dorso-lateral to the aorta. As a 

 general statement, it may be said that the ventral sac supplies the abdominal 

 viscera, while the dorso-lateral sacs supply the retroperitoneal structures the 

 viscera, the body-wall, and the lower extremities although, on account of consider- 

 able overlapping, this generalization must be regarded as only approximate. 



Thus, from the retroperitoneal sac are given off lymphatics which drain the 

 whole or part of the lung, diaphragm, liver and biliary passages, stomach, small and 

 large intestine, capsule of spleen, pancreas, kidneys, Wolffian bodies, gonads, Miil- 

 lerian and Wolffian ducts, and umbilical cord. The dorso-lateral lymphatics that 

 is, the paired iliac sacs drain wholly or in part the diaphragm, body-wall, adrenals, 

 kidneys, bladder, Miillerian and Wolffian ducts, umbilical cord, and the entire 

 posterior half of the body. Only a few structures, notably the diaphragm, the 

 kidneys, and the Miillerian and Wolffian ducts, which later become the excretory 

 canals of the sex-glands, have lymphatics arising from both the ventral and the 

 dorso-lateral sacs. 



On following the development of the lymphatics in these posterior regions of 

 the body, this early system of drainage is found to continue into the adult stage of 

 lymphatic growth. The primary sacs change into lymph-glands which receive 

 afferent vessels from the same organs and structures as did their parent sac. To a 

 considerable extent the position of the primary lymph-glands, differentiated from 

 the primary sacs, falls into two groups the glands ventral and ventro-lateral to the 

 aorta, and those dorsal and dorso-lateral to the aorta. Here, too, in the adult stage 

 of lymphatic growth, the general statement can be made that the organs and 

 structures situated within the abdominal cavity have their lymphatic drainage into 

 the group of glands whose position is ventral or ventro-lateral to the aorta. On the 

 other hand, those structures and organs lying outside of the abdominal cavity, as 

 well as the entire posterior half of the body, have their lymphatic drainage eventually 

 into the group of glands situated dorsal or dorso-lateral to the aorta. 



