FIGURES 116 AND 117 



116 Same, section 41, X 225. 



117 Transverse section through ventral part of upper thoracic region in a 14 

 mm. cat embryo (series 212, slide X, section 4) , X 225. 



3 Right precaval vein. 



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. 



7 Aorta. 



9 Trachea. 

 10 Pulmonary artery. 

 22 Vagus. 

 32 Ventral m^diastinal venous plexus. 



