FIGURES 142 AND 143 



142 Transverse section through ventral part of upper thoracic region in a 15 

 mm. cat embryo (series 216, slide X, section 32), X 225. 



143 Same, section 33. 



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 degen- 



erating embryonal vein. 



7 Aorta. 



8 Oesophagus. 



9 Trachea. 



10 Pulmonary artery. 

 22 Vagus. 



