122 DEVELOPMENT OF THE SYSTEMIC LYMPHATIC VESSELS 



and reconstructed this embryonal venous pathway. While, as 

 previously stated, I differ from the conclusions which he drew in 

 regard to the ontogenesis of the thoracic ducts in the publication 

 quoted, I desire to emphasize the fact that he for the first time 

 clearly defined the para-azygos venous line, which, in my opinion, 

 furnishes the pathway for the subsequent extra intimal develop- 

 ment of the azygos segments of the thoracic ducts. 



He interpreted the thoracic duct in embryos of the domestic 

 cat as a direct caudal prolongation of the jugular lymph sac, de- 

 veloped in the same manner as the latter, through fusion of 

 multiple venous derivatives of the para-azygos venous line above 

 defined. 



His recent work on the development of the systemic lymphatic 

 vessels in the cat, presented before the Second International 

 Anatomical Congress in Brussels, August 7th to llth, 1910, and 

 published in the Proceedings of the Congress, 39 is a revision of 

 the previous publication above quoted, 15 and a return, as regards 

 the genesis of the thoracic ducts, to the original view which we 

 advanced for all systemic lymphatic development in the embryo 

 of the cat in our first joint publication on the subject in 

 1906. 21 



The extraintimal lymphatic anlages of the ducts form along 

 and around the venules composing the ventromedial tributary 

 plexus of the azygos veins, and finally replace them, while in the 

 same way the anterior part of the mesenteric lymphatic net work 

 has its origin in the extraintimal lymphatic spaces which form 

 around the caudal continuation of the ventral plexus, lateral and 

 ventral to the aorta, in the root of the primitive dorsal meso- 

 gastrium. 



It is necessary to exercise great care in the critical stages in order 

 to correctly distinguish between the degenerating vessels of the 

 plexus and the extraintimal lymphatic anlages replacing them, 

 and to compare results obtained from a number of embryos of 



39 C. F. W. McClure: The Extra-intimal Theory and the Development of 

 the Mesenteric Lymphatics in the Domestic Cat (Felis domestica), 6 figs. 

 Anat. Anz., Erganzungsh. z. 37. Bd., Verb. Anat. Ges., 24. Vers., Briissel, 

 1910, S. 101-110. 



