The Origin and Development of the Lymphatic System. 65 



2. Peripheral Lymphatics in Other Forms. 



The pattern of the superficial lymphatics in the human embryo is 

 )wn in the two figs., 505 and 506 (Sahin 134). This was a re- 

 ntable specimen of an embryo 5.5 cm. long which had been kept in 

 •malm some time. On transferring it to freshly made up alcohol, 

 filled the entire superficial lymphatic system. It shows the primary 

 perficial lymphatic plexus. Valves in a few ducts, namely, the 

 ripital, the thoracic and the inguinal, indicate the oldest vessels, 

 le differences between the superficial pattern in the human and in the 

 I are mainly the fact that in the human embryo the thoracic lym- 

 atics are much more prominent, draining into the axilla, while in the 

 I they drain into the superficial cervical plexus, and all the posterior 

 nphatics drain into the inguinal region in the human embryo. In 

 3 human embryo the deep lymphatics for the arm grow from an 

 tension of the jugular sac along the primitive ulnar veins, and the 

 ep lymphatics for the legs grow from the iliac sac along the femoral 

 ins. This shows in fig. 493 (Sabin 134). 



Rabbit and cat embryos are like the human in having a marked 

 velopment of the jugular sac along the primitive ulnar vein (Lewis 

 ). In this respect they differ from the pig where the axillary lym- 

 atics are smaller. In fig. 7 is shown a deep vessel from the jugular 

 2, which is, I think, the axillary duct in the pig. In the rabbit and 

 b cat the axillary sac may possibly arise independently of the jugular 

 2, and in the rabbit a conspicuous chain of peripheral vessels grows 

 )ng the thoraco-epigastric vein (fig. 8, Lewis 76). Injections of cat 

 ibryos show that the axillary lymphatic trunk is very large. 

 The superficial pattern of the lymphatics in bovine embryos, as 

 own by Polinski (107), is much like that of the pig. 

 In the chick the primary lymphatic vessels in the skin connect 

 e posterior lymph heart with the jugular lymph sac along the lateral 

 le in the course of the thoraco-epigastric vein Mierzewski (96) 

 clE. L. Clark (27 and 29). 



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[. ORIGIN AND DEVELOPMENT OP LYMPHATIC GLANDS 

 AND THEIR RELATION TO PRIMARY LYMPH SACS. 



It is easy to prove that the lymphatic sacs in mammals and the 

 gular lymph sac in birds become in part lymph glands. I shall define 

 imary lymph glands as those which are derived from the primary 

 nph sacs. 



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