ON THE FATE OF THE PRIMARY LYMPH-SACS IN THE ABDOMINAL 

 REGION OF THE PIG, AND THE DEVELOPMENT OF LYMPH- 

 CHANNELS IN THE ABDOMINAL AND PELVIC REGIONS, 



Since 1900 interest in lymphatics has been centered about the question of 

 their origin and development. The primary lymph-sacs have been worked out 

 and in general their fate determined. Sabin (1901-2) has shown that the earliest 

 lymphatic buds arise in association with the anterior cardinal veins and form the 

 primary lymphatics in the neck the paired jugular sacs. The other primary sacs 

 originate indirectly from the vena cava through the veins of the Wolffian body. 

 These are the paired iliac sacs, the cisterna chyli (Sabin, 1912) and the retroperi- 

 toneal sac (Lewis, 1906; Baetjer, 1908). Quoting from Sabin (1913): 



"In most general terms the jugular sacs drain the anterior half of the body; the iliac 

 sacs drain the posterior half of the body; while the retroperitoneal or prse-aortic sac drains 

 the viscera. The cisterna chyli with the thoracic duct connects the jugular and renal 

 lymphatics." 



The recent work on the origin of blood-vessels by the differentiation of angio- 

 blasts, or vaso-formative cells from mesenchymal cells (Stockard, 1915; Sabin, 1920; 

 Streeter, 1920), may result in modifying our present conception of the origin of the 

 lymphatics to some such form 'as this: that they arise either directly from the endo- 

 thelium of the veins or in part by a differentiation of new cells analogous to angio- 

 blasts. The experiments of E. R. and E. L. Clark (1920) point in that direction. 

 It is clear, however, that lymphatics begin centrally, close to certain veins, and 

 spread peripherally. 



Considering the sequence in the development of the primary lymphatic system, 

 it was at first thought by Sabin (1901) that the earliest lymphatics in the pig were 

 sacs which bud off from certain veins. F. T. Lewis (1906), going back a step 

 farther, showed that in the rabbit the formation of the primary lymph-sacs is 

 preceded by a plexus of blood-filled capillaries connected with the veins. This was 

 confirmed by Sabin (1912) for pig and human embryos, and by Huntington and 

 McClure (1910) for the cat. Recently E. R, and E. L. Clark (1920) have carried 

 the investigation back still farther in the chick, practically to the beginning, when 

 the first evidence of lymphatics consists of a few blood-filled vessels lined with 

 characteristic lymphatic endothelium and connected with veins. These vessels 

 later join to form a circumscribed continuous plexus of vessels which does not have 

 a continuous lumen and which is still connected with the venous system in a number 

 of places. This plexus is the primordium of the lymph-sacs or lymph-hearts, from 

 which the lymphatics of the body arise and grow peripherally. As stated by Sabin 

 (1913), these buds in connection with veins form "a new type of vessels, namely, 

 lymphatics. These buds unite to form plexuses which develop into sacs. These 

 sacs may become lymph-hearts. From these lymph-sacs or hearts lymphatic 



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