32 



Florence R. Sabin. 



of dull red grapes against the cardinal vein; in the older specimens 

 some of the buds are markedly larger than others, while at 14 mm. 

 the largest of them makes a definite sac with large sprouts projecting 

 dorsalward. At this stage, namely, 14 mm., the sac can be injected 



As- 





Pig. 7. — Injection of the left jugular lymph sac in an embryo pig which 

 measured 18 mm. in its greatest diameter. The specimen was fixed in 10 

 per cent formol and cleared by the Spalteholz method. Magnified about 30 

 times. The glass canula which shows piercing the upper border of the arm 

 bud shows the point of injection. A. c. = anterior curvature of the lymph 

 sac; A. s. = apex of the lymph sac; I. = glass canula used for injection; 

 S. s. = stalk of the lymph sac; V. j. i. = vena jugular interna. 



by direct puncture. The preceding or plexus stage is shown by E. L. 

 Clark for the corresponding sac in the chick in fig. 15. The beginning 

 sac is shown for the human embryo in fig. 491 (Sabin 134). 



It is not easy to get perfect injections by direct puncture, but by 

 the time the embryo is 16 mm. the dorsal sprouts from the sac are 



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