268 GEO. S. HUNTINGTON 



in reference to the main pre- and postcardinal venous lines, in 

 sharp contrast to a regularly disposed metameric series of dorso- 

 medial somatic tributaries draining into the pre- and postcardinal 

 veins. In the later stages we noted that the dorso-lateral ele- 

 ments became confluent to form a large sac, filled with blood 

 and connected with the systemic veins at one or more points. 

 This sac then suddenly evacuated its contents of free blood cells 

 into the veins, separated for a short period from the latter, and 

 then made a secondary connection with them at one or both of 

 two typical points, viz., the angle of confluence of the internal 

 and external jugular veins (common jugular tap) and the jugulo- 

 subclavian angle (subclavian tap). 



In the succeeding stages these sacs made connections with 

 the systemic lymphatic channels, the thoracic ducts, and the ^ 

 lymphatic trunks accompanying the internal and external jugu- 

 lar, the innominate, cephalic and deep cervical veins, and the 

 broncho-mediastinal lymphatic channels. We found that these 

 systemic lymphatic vessels formed as the result of successive 

 centripetal fusion of numerous intercellular mesenchymal spaces, 

 lined by a lymphatic endothelium and developed independently 

 chiefly along the course of the principal veins, or, as notably in 

 the case of the anlages of the thoracic duct and of the mesenteric 

 lymphatics, replacing topographically early embryonal path- 

 ways which in course of further development retrograded or 

 disappeared entirely, e.g., the left azygos vein, the extraperi- 

 cardial portion of left duct of Cuvier, the left post-caval vein. 



This genetic history of the mammalian jugular lypiph sacs, 

 repeated closely in its main lines in avian and reptilian embryos, 

 impresses on these structures a peculiar and definite character, 

 quite distinct both from the true venous channels and from the 

 independently developed systemic lymphatic vessels. In their 

 early anlages they appear more closely related to the veins, in 

 their later stages they form an integral part of the amniote 

 lymphatic apparatus. Their evident topographical and morpho- 

 logical correspondence to the completely developed lymphatico- 

 venous hearts of the lower vertebrates suggested that they func- 

 tioned in this modified and reduced form in the same way, as 



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