384 



The Development of the Lymphatic System 



ducts often have a rim of coagulated lymph which stains in eosin,. 

 and this together with the absence of blood cells aids in distinguish- 

 ing them. 



To return to the diagrams of the lymphatic system. Fig. 9 shows that 



the ducts from the posterior lymph 

 hearts have just reached the skin. 

 If a needle is inserted rather deep- 

 ly over the crest of the ileum, the 

 receptaculum chyli can be injected 

 through them. The diagrams of 

 the lymph hearts show why it is so 

 much easier to inject the anterior 

 one directly than the posterior one, 

 namely, that the anterior one is 

 superficial. To inject the posterior 

 lymph heart directly, the abdomi- 

 nal wall must be opened and the 

 needle inserted just below the kid- 

 ney. There are so many veins in 

 this region, however, that it is rare 

 to get a pure lymphatic injection 

 in this way. The receptaculum 

 chyli is much more easily injected 

 directly than the lymph heart. 



At the stage of this diagram. 

 Fig. 9, the lymph ducts to the- 

 heart have encircled the auricles. 

 In an embryo 3.7 cm. long, lym- 

 phatics have been injected cover- 

 ing the inner surface of the left 

 lung, while in serial sections of an 

 embryo 3 cm. long there is a plexus 

 of lymph ducts in the root of the 

 mesentery, and the right lym- 

 phatic duct can be traced to the 

 right lung. At this stage there 

 has also been a new development in the superficial lymphatics at the 

 neck. The diagram shows simply the two systems growing behind the 

 ear and over the back. The ducts now grow both between the eye and 

 the ear and in front of the eye. This shows in Fig. 1. 



The last two diagrams show the further development both of the- 



Fig. 10. Diagram of the lymphatic 

 system in an embryo pig 4 cm. long. 

 X 3. Adr, adrenal; alh. anterior lymph 

 heart; ao, lymphanc plexus to the aorta 

 wall; arm d, deep lymphatics to the 

 arm; du, ducts to the duodenum; h, 

 ducts to the heart; oe. ducts to the 

 oesophagus; leg d, deep lymphatics to 

 the leg; lu, ducts to the lung; mp, ducts 

 to the mesenteric plexus; plh, posterior 

 lymph heart; ro. receptaculum chyli; st, 

 ducts to the stomach. 



