ON THE ORIGIN" OF THE MESENTEKIC SAC AND THORACIC 

 DUCT IN THE EMBRYO PIG. 



BY 



WALTER A. BAETJER. 



From the Anatomical Lahoratort/ of the Johns Hopkins University. 



The modern literature on the development of the lymphatic system 

 may be said to begin with the publications of Ranvier^ in 1895. Prior 

 to this time, the most widely accepted theory was that the earliest 

 lymphatics existed as spaces in the mesenchyme, which gradually became 

 confluent and formed lymphatic ducts. The first break from this idea 

 came as early at 1868, when Danger^ published his observations on the 

 lymphatics in amphibians. He noted that the lymphatics in tadpoles 

 did not resemble tissue spaces, but had rounded endothelial-lined ends, 

 which often had long strands of endothelium coming from them. This 

 gave them the appearance of developing blood-vessels, and Langer inter- 

 preted his observations to mean that lymphatics grow like blood-vessels 

 by the sprouting of endothelium. 



Ranvier noted the same appearances in the developing lymphatics in 

 tadpoles and in pig embryos and also interpreted them to mean that the 

 lymphatic vessels grow by budding. This made the original theory seem 

 even more doubtful and suggested the close association between the 

 lymphatics and the veins. The proof of the venous origin of the lym- 

 phatics — suggested by Ranvier — was not definitely established, how- 

 ever, until the work of Dr. Sabin^ on pig embryos in 1902. In this 

 study it was first shown that the lymphatic system begins by the forma- 

 tion of sacs or hearts, which arise from the veins. Four of these sacs 

 were described — two in the neck and two in the posterior portion of the 

 body, from which lymphatic vessels grew out and invaded the rest of 

 the body. 



^Ranvier. Comptes-Rendus de rAcademie des Sciences. Tome 121, 1894, 

 1895 and 1896, and Arch. d'Anatomie, 1897. 



"Langer. Sitz. d. k. Akad. d. Wissensch., Bd. LVII, 1868. 

 *Sabin. Am. Jouk. Anat., Vol. I. 



The American' Journal of Anatomy. — Vol. VIII. Xo. 3. 



