FIGURE 12 



12 Transverse section of anterior thoracic region in a 14 mm. embryo (series 

 127, slide VIII, section 12), X 225. 



4 Atrophying embryonal vein, forming kernel in interior of develop- 



ing and replacing lymphatic space. 



5 Extraintimal or perivenous lymphatic space surrounding degen- 



erating embryonal vein. 



6 Precardinal or precava, resp. azygos of left side. 

 6' Left azygos vein, thoracic portion. 



7 Aorta. 



8 Oesophagus. 



