70 



Florence R. Sabin. 



enlarged, others reduced and dropped out, while still others are 

 changed into lymphatic sacs. 



The next embryo of the series (No. 317), measuring 121/2 cm., 

 has not been illustrated because it is exactly like the preceding except 

 that the lymphatics have much less blood, and the plexus along the 





Fig. 7 



Fig. 8 



Fig. 7. Coronal section through the arm bud of a human embryo, 11 mm. 

 long. Mall collection, No. 353, to show the plexus of veins or lymphatic 

 sacs along the internal vein. This section is to be related to Fig. 8 by means 

 of tlie composite section, Fig. 9. X about 36. S. 1. j., saccus lymphaticus 

 jugularis ; "V. c, vena cephalica ; V. j. i., vena jugularis interna. 



Fig. 8. Coronal section through the arm bud of the same embryo as Fig. 

 7, to show the relation of the lymphatic sac to the primitive ulnar vein. 

 The larger lymphatic sac is the upper part of the extension along the prim- 

 itive ulnar vein, shown in Fig. 18. x about 36. S. 1. j., saccus lymphaticus 

 jugularis ; V. c, vena cephalica ; V. j. i., vena jugularis interna ; V. t. 1.. 

 vena thoracicus lateralis; V. u. (p.), vena ulnaris (primitiva). 



jugular vein has been definitely transformed into a single sac. The 

 extent of the lymphatics along the jugular vein is practically the 

 same. The valve is definite, showing the same type as seen in Fig. 



