The Origin and Development of the Lymphatic System. 63 



)ng have been injected from one puncture. This is a complete injec- 

 ion, which it is clear that fig. 16 is not. In fig. 5 (Sabin 130) for 

 xample the lymphatics between the eye and ear are terminal ducts. 



Good examples of the anastomoses of different groups of lymphatics 

 re shown in fig. 16 in the vessel which connects the submaxillary 

 nd the facial plexus; moreover the thoracic, cervical and brachial 

 ilexuses are continuous. 



In the embryo pig from 5 to 5.5 cm. long there are no valves in the 

 ucts. It is also the stage of the simple primary plexus of lymphatics, 

 n fig. 16 a secondary plexus of finer lymphatics is growing more 

 uperficially and by the time the embryo is from 6 to 7 cm. long 

 here is a deep plexus with valves and a finer-meshed superficial plexus. 



The relation of the jugular lymph sacs to lymph glands is shown in 

 ig. 17. Here it is clear that the sac" stalk and anterior curvature lie 

 ieneath the sternocleidomastoid muscle and that the apex of the 

 ac lies in the posterior triangle of the neck. That the cervical plexus 

 s now a lymph gland is clear, and there is a facial and submaxillary 

 land also. The cervical plexus becomes a group of glands. 



The account of the peripheral lymphatics from the jugular sacs is. 

 lot complete without mention of the lymphatics of the heart and lungs. 

 Niese lymphatics have not yet been worked out, but it can be said that 

 here are two sets of lymphatics for the lungs, the deep and the super- 

 icial or pleural. The deep lymphatics develop from the jugular sacs ; 

 hey follow the trachea and are present in a pig measuring 23 mm. 

 nd a human embryo measuring 20 mm. I have not injected them and 

 rhen reconstructed they show the Mayer-Lewis anlagen; that is, in 

 econstruction they split into a chain of beads. The pleural lymphatics 

 '. have injected from the retroperitoneal sac, through the diaphragm 

 o the caudal surface of the lung. Injections of the thoracic duct as, 

 or example, fig. 7 (Nuck 100), also shows vessels from the thoracic duct 

 o the lung. Therefore the lung seems to have a double supply of lym- 

 thatics, part from the jugular sac and part from the renal sacs by 

 ray of the diaphragm and by way of the thoracic duct. 



B. THE PERIPHERAL LYMPHATICS FROM THE RENAL SACS. 



The retroperitoneal sacs give rise to the lymphatics of the abdominal 

 iscera except the kidney3. The sac as it lies in the root of the mesen- 

 ery has been figured by Heuer (43). It spreads over the ventral 



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