3^0 The Development of the Lymphatic System 



cords develops the lumeu of the thoracic ducts which forms connec- 

 tions with the ductus Botali, the aorta and the superior vena cava. 



In the present communication, Eanvier's hypothesis that the lym- 

 phatic system takes its origin from the veins Avill be proved. He 

 missed the proof because he thought there were no lymphatics in pig 

 embryos under 9 cm.° As a matter of fact the ducts have spread over 

 nearly the whole body in a pig 5.5 cm. long. 



In the study herein reported, I have been greatly aided by a manu- 

 script of Dr. W. G. MacCallum's which I was privileged to read. From 

 this paper, which is on " The Kelations between the Lymphatics and 

 the Connective Tissue/' and is soon to be published in the Archiv fiir 

 Anatomic, certain observations ?nd conclusions which aid my work are 

 quoted with the author's permission. 



He injected the subcutaneous lymphatics of embryo pigs for the 

 most part between 5 and 15 cm. long and has given most graphic 

 and accurate descriptions of these injections, and of the lymphatics 

 both in fresh and stained preparations. He noted as Eanvier had the 

 growth of the lymphatic capillaries within the plexus by budding, and 

 describes the long sprouts or strands of endothelial cells growing out 

 from the ducts, and how the lumen of a duct gradually opens into 

 the sprouts. He discovered the fact that the early lymphatics have 

 no valves, and made an important addition to the method of injec- 

 tion, by stripping off the skin, placing it on a slide and injecting it 

 under the microscope. He noted that the fluid injected ran into per- 

 fectly definite walled channels and that there was no extravasation 

 until the pressure was too great, when the walls of the ducts would 

 suddenly and explosively burst and the fluid would then pass into 

 the meshes of the connective tissue. His conclusion was that the 

 lymphatic ducts in the skin of the embryo pigs are closed ducts. 

 ' Inasmuch as in this communication the lymphatic system of the 

 mammal will be traced in its development up to the stage represented 

 in the frog, it will be necessary to keep in mind the amphibian lym- 

 phatic system. In the frog the large subcutaneous lymph sacs com- 

 municate by ducts with four lymph hearts or sacs, two in the neck 

 and two in the inguinal region. From these sacs, ducts empty into 

 the veins in four places, two in the neck at the junction of the sub- 

 clavian and cardinal veins, and two in the inguinal region, where the 

 femoral and sciatic veins join to enter the Wolffian body as the renal 

 portal system. There are no valves except Avhere the ducts enter the 

 veins and there are no lymph glands. 



6Ranvier: Comptes Rendus, Tome 131, 1895, p. 1106. 



