162 Transverse section of upper thoracic region in a 14 mm. cat embryo 

 (series 210, slide IX, section 26), X 200. 



163 Dorsal portion of same section, X 225. 



1 Sympathetic nerve. 



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. 



7 Aorta. 



17 Prevertebral venous plexus. 



22 Vagus. 



32 Ventral mediastinal venous plexus. 



33 Left subclavian artery. 

 40 Innominate vein. 



