DE^'ELOPMENT LYMPHATIC SYSTEM IN AMNIOTES 267 



the adult lymphatico-venous connection or connections. Both 

 of these views seem to have been entertained, at different times, 

 by the advocates of the centrifugal theory. 



If, on the other hand, the vertebrate lymphatic system devel- 

 ops according 'to the tenets of the second or 'centripetal' theory 

 above outlined, the question of the establishment of the adult 

 lymphatico-venous connections becomes exceedingly important. 

 If independently developed para-haemal lymphatic anlages de- 

 velop as intercellular spaces in the embryonal mesenchyme and 

 then unite with each other to form a connected and continuous 

 system of lymphatic channels, this system must make necessarily 

 secondary connection or connections with the veins at definite 

 and constant angles of venous confluence, corresponding to the 

 known adult types of lymphatico-venous communication. In 

 the embryos of all three amniote classes this secondary con- 

 nection is effected in the anterior part of the body through the 

 jugular lymph sac, representing a modified and rudimentary 

 anterior lymph-heart. 



The development of this structure has been studied in the 

 mammalian embryo by Sabin (16, 17) (pig, man), F. T. Lewis 

 (18) (rabbit) and McClure and myself (19) (cat). My colleague, 

 Prof. A. M. Miller, has traced its developmental history in the 

 chick (20), and I have done so in chelonian and lacertilian 

 embryos (12). 



All of these investigations revealed a very close and intimate 

 association of this segment of the lymphatic apparatus with the 

 pre- and postcardinal veins adjacent to and including their 

 confluence at the Cuvierian junction. 



The early anlages of the jugular lymph-sacs in mammalian, 

 avian and reptilian embryos appear as an intricate plexus of 

 vascular channels and spaces, for the most part filled with blood 

 cells and in certain stages in free communication with the sys- 

 temic veins. 



When McClure and I published the results of our joint inves- 

 tigation on the development of the jugular lymph-sacs in embryos 

 of the domestic cat, in 1908 and 1910 (19), we described these 

 vascular anlages of the sacs as occupying a dorso-lateral position 



