FIGURES 186 AND 187 



186 Transverse section of left upper thoracic region in a 13.5 mm. cat 

 embryo, (series 223, slide VIII, section 39), X 225. 



187 Same, section 40. 



1 Sympathetic nerve. 



4 Atrophying embryonal vein, forming kernel in interior of developing 



and replacing lymphatic space. 



5 Extraintimal or perivenous lymphatic space surrounding degenerat- 



ing embryonal vein. 



8 Oesophagus. 



9 Trachea. 

 22 Vagus. 



33 Left subclavian artery. 



40 Innominate vein. 



41 Vertebral artery. 



43 Costo-cervical artery. 

 45 Innominate artery. 



