74: Florence R. Sabin. 



no traces of the other sacs in the posterior part of the body. The 

 veins are especially large in the posterior part of the body. The 

 sections are too thick to show the valves well. The sacs appear as in 

 Fig. 3 except that they are larger. 



The next embryo of tlie series (iSTo. 22) measures 20 mm. and 

 shows several interesting points. The series is cut transversely and 

 the sacs also appear much as they are shown in Fig. 3 for an embryo 

 10.5 long except that they are much wider. The sacs measure 

 1.6 x 7. The new point of interest is, that in this series the third 

 nerve cuts through the sac ; in a later stage, in an embryo measuring 

 30 mm., Fig. 12, three nerves cut through the sac, namely the third, 

 fourth and fifth. For the first time, in this stage, there are vessels 

 extending from the sac toward the skin. It will be remembered that 

 this is the point in which the recent American workers on the 

 lymphatic system differ. 



A further point of interest in this series is a group of small ves- 

 sels along the renal anastomosing vein. These vessels, I think, are 

 forerunners of the mesenteric sacs. The indications of lymphatics 

 for the posterior part of the body appear at this stage. 



In another embryo CNo. 128) measuring 20 mm. the jugular 

 sacs are again abortive, measuring only .75 mm. The specimen is, 

 however, very interesting in connection with the lymphatics for the 

 posterior part of the body. In the neck, as we have seen, the early 

 lymphatics are the two jugular sacs, with either an extension or 

 a supplementary sac along the primitive ulnar vein, in the arm bud. 

 In the posterior part of the body three sacs have been found, two 

 of them median, the mesenteric sac and the cistema chyli ; and one 

 paired, namely the posterior lymph sac. In this embryo, in the 

 place of the future cistema chyli, there is an extensive median vein 

 connecting the two sciatic veins. Just ventral to this, compare with 

 Fig. 12, is the renal anastomosis running through the great mass 

 of the sympathetic system in the hilum of the two adrenal bodies. 

 Around these two large median anastomosing veins there is as yet 

 no evidence of the future median lymphatic sac. However, to the side 

 of the two sciatic veins, just posterior to the median anastomosis, is an 

 abundant plexus of veins on the one side and a possible beginning pos- 



