THORACIC DUCT DEVELOPMENT IN THE PIG 



457 



12d 



12 s 



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Fig. 27 Transverse section through the anterior supracardinal region in a 

 26 mm. pig embryo (series 69, slide 53, section 10), X 150. 5d,5s, right and left 

 thoracic ducts; 12d, 12s, right and left supracardinal veins; 13, aorta; 14, sympa- 

 thetic nerve trunk. 



only after the thoracic duct has lost its multilocular and plexi- 

 form character, and its channel approaches more nearly to a 

 clear-cut and simple tube (5s, fig. 27). The manner in which the 

 mesenchymal cell is transformed into an endothelial cell occurs 

 undoubtedly, as Huntington has suggested, by a mechanical 

 adaptation to the pressure of the fluid within the lymphatic 

 cavity. This view is entirely in harmony with the conditions 

 observed in the extra-embryonic area of the chick 23 where the 



23 At the last session of the American Association of Anatomists, December 27, 

 1911, at Princeton, N. J., John E. McWhorter and Allen O. Whipple of the College 

 of Physicians and Surgeons, Columbia University, presented a report on the devel- 

 opment of the blastoderm of the chick in vitro. This report appeared as a short 

 preliminary paper with twelve figures in the Anatomical Record, vol. 6, no. 3, 

 March, 1912. These investigators, on the basis of a study of the living growing 



