PLATE 3 



EXPLANATION OF FIGURE 



30 Reconstruction of the lower cervical and thoracic regions in a 23 mm. pig 

 embryo (injected series 23a, Johns Hopkins University Embryological Collec- 

 tion, slides 21-30 inclusive), X 50. Dorsal view, slightly from the left. 



A, precardinal division 



B, postcardinal division 



C, supracardinal division 

 1, left jugular lymph sac 



S, anterior lymphatic plexus or subse- 

 quent common trunk of the right 

 and left thoracic ducts. 



5d, 5s, continuous and injected portions 

 of the right and left thoracic duct 

 anlagen 



X,X, extent of the continuity of 5d and 

 5s, and the farthest points to which 

 the injection mass has penetrated 



4d, long and short lymphatic spaces in 

 the axis of the injected anlage and 

 in the path of the future right thor- 

 acic duct 



4s, lymphatic spaces in the left thoracic 

 duct line hidden by the veins, but 

 indicated by the dotted circles 



7, oblique vessel, degenerating ante- 

 riorly 



8, dorsal segmental veins of the pre-, 

 post, and supracardinals 



9, internal jugular vein 



10, left precardinal vein 



lid, lis, right and left postcardinal 



veins 

 121s, left supracardinal line, plexiform; 



the right line has fused with the right 



postcardinal vein 

 12d, 12s, right and left supracardinal 



veins 



13, aorta 



13s left subclavian artery and branches 



14, left sympathetic nerve trunk 



15, vagus 



16, recurrent laryngeal nerve, and ac- 

 companying vein 



17, oesophagus 



20, anterior tip of left mesonophros 



21, left Cuvierian duct 



22, left subclavian vein 



23, cephalic vein 



24, external jugular vein 



25, degenerating segments of the for- 

 mer extensive plexus between the 

 supracardinal lines 



26, subclavian approach of the jugular 

 lymph sac 



470 



