FIGURES 264 AND 265 



264 Same, section 8. 



265 Transverse section of middle thoracic region in a 19 mm. cat embryo, 

 (series 253, slide XXIV, section {)) X 225. 



1 Sympathetic nerve. 



3^ Right azygos vein, thoracic portion. 



4 Atrophying embryonal vein, forming kernel in interior of developing 



and replacing lymphatic space. 



5 Extraintima,! or perivenous lymphatic space surrounding degen- 



erating embryonal vein. 



6 Left azygos vein, thoracic portion. 



7 Aorta. 



8 Oesophagus. 



15 Interazygos venous plexus. 

 34 Ventro-medial azygos plexus. 

 36 Thoracic duct, azygos segment. 



