486 



A. M. MILLER 



4 12 



Fig. 7 From a photograph of a transverse section through the upper thoracic 

 region of a chick embryo of seven days. 1, Precardinal vein; 4b, branch of verte- 

 bral vein; S, prelymphatic sac; 6a, aortic arch; 7, oesophagus; 8, notochord; 9, 

 spinal nerves; 9b, vagus nerve, with the ganglion nodosum on the right; 10a, 

 trachea; 12a, branch of vertebral artery. 



Chick embryo of eight days and fourteen hours. Reconstruction, 

 right side. Fig. 8. Passing on to a considerably older embryo 

 (eight days and fourteen hours), we find the lymph sac appar- 

 ently at the height of its development. It consists here of an 

 elongated bag (5) extending some distance cephalad from the 

 level of the subclavian vein (14-)' Its caliber is approximately 

 equal to that of the jugular (precardinal) vein (1). Situated 

 ventral to the brachial plexus of nerves {9a), which indents 

 its dorsal wall, it lies in close apposition to the dorsal surface of 

 the jugular vein. The ganglion nodosum of the vagus nerve 

 indents its mesial wall. Its length is about 1.5 mm. and its great- 

 est diameter about 0.5 mm.' 



^ These measurements were computed from the number and thickness of the 

 sections involving the lymph sac. 



