488 



A. M. MILLER 



10 



16 



Fig. 9 From a photograph of a transverse section through the upper thoracic 

 region of a chick embryo of eight days and fourteen hours. 1, Precardinal vein; 

 4a, vertebral vein; 5, jugular lymph sac with tap at 5a on the right; 6a, common 

 carotid artery; 7, oesophagus; 8, notochord; 9b, vagus nerve; 10a, trachea; H, 

 subclavian \ein; 16, subclavian artery. 



The sac at this stage, having acquired a secondary and new con- 

 nection with the venous system, may be properly spoken of as 

 the lymph sac. The new communication with the jugular (pre- 

 cardinal) vein (1) is established on the dorso-mesial aspect of 

 the vein about opposite the opening of the subclavian (fig. 8, 

 6a and fig. 9, 5a). The conditions in this particular stage indi- 

 cate that the union has taken place merely through apposition of 

 the wall of the sac with the wall of the vein and a subsequent 



