FIGURES 10 AND 11 



10 Transverse section of anterior thoracic region of 12 mm. cat embryo (series 

 217, slide X, section 12), X 225 showing early extraintimal lymphatic develop- 

 ment. 



11 Transverse section of anterior thoracic region in a 12 mm. cat embryo (series 

 211, slide X, section 15), X 225. 



3 Precardinal or precava, resp. azygos of right side. 



4 Atrophying embryonal vein, forming kernel in interior of developing 



and replacing lymphatic space. 



5 Extraintimal or perivenous lymphatic space surrounding degenerating 



embryonal vein. 



6 Precardinal or precava, resp. azygos of left side. 



7 Aorta. 



8 Oesophagus. 



9 Trachea. 



10 Pulmonary artery. 

 22 Vagus. 



