PLATE 2 



EXPLANATION OF FIGURE 



29 Reconstruction of the vascular channels of the lower cervical and thoracic 

 regions in a 20 mm. pig embryo (series 194, slides 22-31 inclusive), X 50. Sinistro- 

 dorsal view. 



A, precardinal division 



B, postcardinal division 



C, supracardinal division 



1, left jugular lymph sac 



2, thoracic duct approach 



3, anterior lymphatic plexus or sub- 

 sequent common trunk of the right 

 and left thoracic ducts replacing the 

 precardinal veno-lymphatics 



4d, lymphatic spaces in the right thor- 

 acic duct line replacing the oblique 

 vessel 



4s, lymphatic spaces in the left thoracic 

 duct line 



6a, precardinal veno-lymphatics 



7, oblique vessel, degenerating and 

 breaking up into segments 



6b, postcardinal veno-lymphatics 

 6c, supracardinal veno-lymphatics 



8, dorsal segmental veins of the pre-, 

 post-, and supracardinals 



9, internal jugular vein 



10, left precardinal vein 



12d, lis, right and left postcardinal 

 veins 



12d, 12s, right and left supracardinal 



veins 

 I2ls, left supracardinal line; right line 



has completely fused with the right 



postcardinal 

 IS, aorta 



13b, ductus arteriosus Botalli 

 13s, left subclavian artery and branches 



14, left sympathetic nerve trunk 



15, vagus 



16, recurrent laryngeal nerve 



17, oesophagus 



21, left Cuvierian duct 



22, left subclavian vein 



23, cephalic vein 



24, external jugular vein 



25, degenerating remnants of the former 

 venous plexus between the supra- 

 cardinal lines. 



26, subclavian approach of the jugular 

 lymph sac 



N5, fifth spinal nerve 



468 



