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Fig. 14 Transverse section through the left lower cervical region in a 23 mm- 

 pig embryo (series 23a, J.H.E.C, slide 21, section 16), X 200. 3, anterior lympha- 

 tic plexus of the thoracic duct injected; Ex, extravasations of the injection sub- 

 stance into the surrounding mesenchyme; 9, internal jugular; 14, sympathetic 

 nerve trunk; 17, oesophagus. (Reconstruction, fig. 30.) 



The discontinuous fusiform lymphatic space (4-d) is of consider- 

 able length, capable of being followed through thirty-seven sections 

 (thickness of sections: 20 micra), and it is variable in diameter (figs. 

 31, 15, 16 and 17), at times being very broad and at other times 

 narrow and not so sharply demarcated from the intercellular 

 lacunae of the mesenchyme surrounding it. In form it is very 

 irregular, and its lumen is often bridged by tissue strands of 

 greater or lesser thickness which give to it a multilocular appear- 

 ance as shown in cross-section in figures 16 and 17 (4-d). This 

 condition and the fact that it is bounded by ordinary mesen- 

 chymal cells supply strong proof against its venous origin. The 

 difference between its lining and that of the neighboring venules 

 (25) and veins is strikingly expressed even in figure 15, in which its 

 boundary is quite regular and clear-cut but the greater delicacy 



