THORACIC DUCT DEVELOPMENT IN THE PIG 407 



hearts arise by the coalescence along the internal jugular vein 

 of several venous outgrowths which become detached to form a 

 large isolated sac. A similar process was observed in the posterior 

 part of the body in the region of the subcardinal and mesenteric 

 veins. He also discovered a chain of discontinuous 'lymphatic 

 spaces' or endothelial-lined anlagen, apparently detached venous 

 outgrowths, situated along the azygos veins and in the path of the 

 future thoracic duct. From their position and consecutive arrange- 

 ment he concluded that they fuse with one another and the 

 jugular and mesenteric sacs and thus produce the continuity of 

 the duct. To quote his own words: "The study of the specimens 

 seems to show that the lymphatics along the aorta (thoracic 

 ducts) are derived in part from the azygos veins; below from the 

 subcardinal; and above from the jugular sacs." It is also of 

 importance to state here that the 'lymphatic spaces' which he 

 described are 'scarcely distinguishable from blood vessels.' 



In 1907, shortly after the work of Lewis, Huntington and 

 McClure made a more detailed and extensive study of the develop- 

 ment of the jugular lymph sacs and confirmed in the main his 

 results. 8 They had formerly believed that the sacs arise by the 

 formation, enlargement and fusion of perivascular spaces, 9 but 

 now, from the data of a large number of beautiful and accurate 

 wax reconstructions of cat embryos, they established the opinion 

 that they come from the precardinal and in part from the post- 

 cardinal veins by the confluence of a series of outgrowths or 

 derivatives which they called veno-lymphatics, as suggesting 

 their venous origin and their subsequent transformation into a 

 lymphatic structure. For a short time McClure also carried 

 this conception to the developing thoracic duct, 10 agreeing with 

 Lewis in the formation of a chain of discontinuous anlagen along 



8 George S. Huntington and Charles F. W. McClure: The anatomy and develop- 

 ment of the jugular lymph sac in the domestic cat. Anat. Rec. vol. 2, 1908, pp. 

 1-18. Am. Jour. Anat., vol. 10, no. 2, April, 1910, pp. 177-311. 



9 George S. Huntington and Charles F. W. McClure: The development of the 

 main lymph channels of the cat in their relation to the venous system. Am. Jour. 

 Anat., vol. 6, 1907. Abstr. Anat. Rec, vol. 1, pp. 36-41. 



10 Charles F. W. McClure: The development of the thoracic and right lymphatic 

 ducts in the domestic cat. Anat. Anz., Bd. 32, nos. 21 and 22, 1908, pp. 534. 



