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A. M. MILLER 



(fig. 3) rapidly increase, assume a more plexiform character, 

 successively amalgamate with one another, and become separated 

 from the permanent veins, until the conditions shown in figs. 

 4 and 5 are attained. 



Fig. 6 Diagram drawn from a reconstruction of the veins, prelymphatic sac 

 and nerves in the upper thoracic region of a chick embryo of seven days. Right 

 side. /, Precardinal vein; 3, duct of Cuvier; 5, prelymphatic sac; 9a, brachial 

 plexus; 14, subclavian vein. 



Chick embryo of seven days. Reconstruction, right side. Fig. 6. 

 Out of the complicated plexus of channels present in the six day 

 embryo (fig. 4, 5) there has arisen a quite definite sac-like struc- 

 ture, which extends cephalad from the level of the duct of Cuvier 



