Florence E. Sabin 377 



lymph ducts in pigs 4 to 6 cm. long were injected and the specimens 

 were dissected so as to follow the ducts to the vein. When, however, 

 the injection had gone over into the veins extensively the lymph ducts 

 could not be distinguished from them. To overcome this dilficulty the 

 veins were filled with cinnabar gelatine and then the lymphatics were 

 injected with a small amount of fluid, just enough to enter the vein. 

 It is easy to see when the Berlin blue enters the subclavian vein, for the 

 vein lies so near the surface. These specimens showed that the duct 

 accompanies the anterior cardinal vein. In 



embryos between 18 mm. and 2.5 cm. long, /"^ " ~"X 



if one injects subcutaneously in the side of / , \ 



the neck, small ducts pass inward and open 7,, \ 



into a large sac just external to the cardinal 

 vein. The sac when injected is easily seen 1 \v " --. /) 



from the surface. Figure 3 is a section \ H Jp\ U. iVcv 



through it in an embryo 2.5 cm. long. . This ^ 1 _..„.^ ^ / 



sac, which corresponds to the anterior '1|* 



lymph heart of the frog, is the key to the fj^ure 3. Transverse section 



study of the subcutaneous lymphatics for i^S^t^lHl^rtt anfel-ilfr lymTh 

 the anterior half of the body, for they all tTh'"" ll.'^'f^^^^V'^ri^li 

 radiate from it. In serial sections of this pfiThk^nxfrtrachir''*' ^'"''*' 

 stage, the duct from the sac to the vein was 

 traced to the junction of the anterior cardinal and subclavian veins. 



This method was sufficient as long as the sac could be injected from 

 the surface, but in an embryo below 18 mm. in length it was again 

 difficult to distinguish the l3^mphatics from the veins. To overcome 

 this difficulty the veins Avere now injected. This can be done in three 

 ways: First, if the umbilical cord is tied, there will be a natural injec- 

 tion of blood; second, if one injects into the liver the entire venous 

 system will be injected, and third, in the younger embryos in which 

 the liver is too small the "Wolffian body answers the same purpose. By 

 this method the sac which, being empty, contrasted with the injected 

 vein was traced in serial sections in an embryo 15 mm. long. 



Serial sections were now cut of embryos 12, 13 and 14 mm. long 

 and showed no lymphatics whatever. However, in an embryo 14.5 cm. 

 long a minute lymphatic sac connected with the vein was found. There 

 are Avell marked differences in development between embryos 14, 14.5 

 and 15 mm. long. An embryo 15 mm. long shows the ear (See Keibel's 

 ISTormaltafeln, No. 1. Bas Sehwein. Fig. 23), while an embryo of 14 

 mm. corresponds more to Keibel's Fig. 21, and shows indistinctly all 

 four visceral arches. In the sections of the embryo 14 mm. long the 



