The Origin and Development of the Lymphatic System. 63 



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

 tion, which it is clear thai fig. 16 is not. In fig. 5 (Sabin L30) for 

 example the lymphatics between the eye ami ear are terminal ducts. 



Good examples nf the anastomose- of different groups of lymphatics 

 are shown in fig. l(j in the vessel which connects the submaxillary 

 ami the facial plexus; moreover the thoracic, cervical ami brachial 

 plexuses are continuous. 



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

 ducts. It is also the stage of the simple primary plexus of lymphatic-. 

 In fig. 1G a secondary plexus of liner lymphatics is growing more 

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

 there 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 

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

 beneath the sternocleidomastoid muscle and that the apex nf the 

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

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

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



The account of the peripheral lymphatics from the jugular sacs is 

 not complete without mention of the lymphatics of the heart and lungs. 

 These lymphatics have not yet been worked orft, but it can be said that 

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

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

 they follow the trachea and are present in a pig measuring v'.'i mm. 

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

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

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

 I have injected from the retroperitoneal sac, through the diaphragm 

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

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

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

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

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



R. THE PERIPHERAL LYMPHATICS FROM THE RENAL SACS. 



The retroperitoneal sacs give rise to the lymphatics of the abdominal 

 viscera except the kidney-. The sac as it lies in the mot of tin mesen- 

 tery has been figured by lienor (4-' ? >). It spreads over the ventral 



