406 OTTO F. KAMPMEIER 



ever, she did not describe or figure the details or factors of this 

 growth, except to say that the lymph vessels at first bud from 

 the veins and thereby derive their endothelium from them and 

 then continue to grow distally apparently by the proliferation of 

 their cells. The sprouting and elongation of the thoracic duct is 

 indicated in three diagrams constructed from embryos of 20, 27, 

 and 30 mm. In the first of these schemes the right lymphatic 

 and thoracic ducts are seen as two short caudal extensions from 

 the jugular lymph sacs. In the second, they have become longer 

 and the left one or thoracic duct has divided into two branches, 

 one of which passes to the right side of the aorta as the rudiment 

 of the right thoracic duct, and the other remains on the left side 

 as the left duct. In the diagram of the 30 mm. embryo these two 

 branches have extended far back and have established continuity 

 with the cisterna chyli and the posterior lymph hearts, thus com- 

 pleting the thoracic duct system. 



A few years later, in 1906, F. T. Lewis made public a short 

 account of the development of the lymphatic system in rabbit 

 embryos. 7 His results are of great interest because they repre- 

 sent a new conception of the genesis of the lymphatics, being 

 neither identical with the centrifugal growth theory of Sabin 

 nor with the theory of their direct mesenchymal origin, but in a 

 sense standing between these two. Furthermore, he was the 

 first investigator to determine the principle involved in the forma- 

 tion of the lymph sacs and to point out certain definite events 

 preparatory to the completion of the thoracic duct in the mamma- 

 lian embryo. In this studies on the transformation of the venous 

 system in the posterior regions of rabbit embryos, he noticed that 

 portions of the subcardinal veins became isolated and seemingly 

 converted into lymphatic vessels. He found more and more of 

 these so-called detached 'lymphatics,' and led by this suggestion, 

 he took up a more systematic investigation of the pathways of 

 the larger systemic lymphatics of the body. He made a number of 

 serial graphic reconstructions and thereby brought to light some 

 very interesting results. He observed that the jugular lymph 



7 Frederic T. Lewis : The development of the lymphatic system in rabbits. Am. 

 Jour. Anat., vol. 5, 1905, pp. 95-111. 



