50 Florence B. Sabin. 



that describes models better than the actual process of growth by sprout- 

 ing by which the veins are formed. 



Some of the figures of the models from embryos measuring 7 mm., 

 for example fig. 33, represent lymphatics in the early plexus stage; 

 I do not, however, find any mention of the presence of blood. Figure 

 46 shows the beginning of the enlarging of the plexus into sacs. From 

 their later stages figs. 46 to 65, but much better from Lewis, fig. 6 

 (76), can be made out the especial characteristics of the jugular 

 sacs in the cat. They are (1) that the jugular sac in the cat arises 

 from the posterior cardinal vein as well as from the anterior cardinal 

 vein. This point is well shown in Huntington and McClure figures. 

 (2) The cerebral end of the ventral or jugular portion of the sac is 

 very large. This is the part that drains the larynx. (3) The internal 

 jugular trunk is small. (4) The dorsal apex of the sac which lies 

 in the posterior triangle of the neck is large. (See Lewis' fig. 6.) It 

 is connected with the cerebral end by a slender vessel. In injections 

 of the sac in embryos between 30 and 60 mm. long it looks very much 

 like the sac in a bovine embryo as shown by Polinski (107) in his fig. 

 7. It lies nearer the arm than the corresponding portion of the sac 

 in the pig. (5) There is a large extension though possibly a dis- 

 tinct sac (Lewis, fig. 6). along the primitive ulnar and thoraco-epi- 

 gastric veins. This sac is very conspicuous in older stages, extending 

 into the axilla and receiving large trunks from the thoracic wall. 

 This makes the jugular lymphatic sac in the cat more like the human 

 than the pig (sec. V). 



The segmental divisions of the sac as indicated by colors in the 

 Huntington and McClure figures are arbitrary and not as valuable 

 as the divisions I have just given, which correspond to the function 

 of the different glands which develop from the sac. 



Lewis' figure also shows a very interesting view of the retroperito- 

 neal and iliac sacs as a continuous plexus, which again emphasizes 

 the fact that the renal sacs anastomose with each other. 



5. Primary Lymphatic System in Birds, Posterior Lymph 

 Heart and Jugular Lymph Sac. 



The history of our knowledge of the lymphatic system in birds is 

 most interesting. The early discoveries of the posterior lymph hearts 

 by Panizza, A. F. J. Mayer, and Stannius, as well as the work of 



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