DEVELOPMENT OF THE THORACIC DUCT 151 



the oesophagus (8), trending sinistro-cephalad into the line of 

 the preazygos segment (35, in figs. 271 and 272). 



Reference to the dorsal view of the reconstruction of this em- 

 bryo (fig. 171) shows that the azygos segment of the thoracic 

 duct (36) has united with part of the caudal division of the preazy- 

 gos chain of lymphatics (35), cephalad of the interazygos anasto- 

 mosis, into a continuous lymphatic channel, although the con- 

 tinuity with the main preazygos segment has not yet been com- 

 pletely established. In other words this condition has been very 

 nearly, but not quite, attained. Some of the preazygos elements 

 (35) have already fused with the azygos segment, thus carrying 

 the latter cephalad beyond the interazygos anastomosis into the 

 territory of the preazygos portion of the thoracic duct. 



