FIGURES 206 AND 207 



206 Transverse section through middle thoracic region in a 13.5 mm. cat 

 embryo, (series 76, slide XT, section 15) X 300. 



207 Same, section 16. 



3 Right azygos vein, thoracic portion. 



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



ing and replacing lymphatic space. 



5 Extraintimal or perivenous lymphatic space surrounding degener- 



ating embryonal vein 



7 Aorta. 



8 Oesophagus. 



15 Interazygos venous plexus. 



