THE DEVELOPMENT OF THE LYMPHATICS IN THE 

 SMALL INTESTINE OF THE PIG. 



GEORGE HEUER. 

 From the Anatomical Laboratory of the Johns Hopkins University. 



With 17 Figures. 



The recent American work on the lymphatic system has given 

 lis a new conception of the morphology of the system as a whole. 

 The primitive lymphatic system consists of a number of sacs which 

 are derived from the veins and which become united into a system 

 for the most part by the thoracic duct. A further essential of this 

 primitive system is that all of the sacs give up their connection 

 with, the veins, and only the two in the neck rejoin the vein to 

 form the permanent opening. Thus far three sets of paired sacs 

 and two unpaired ones have been described: the jugular sacs, the 

 subclavian which in human embryos are an extension of the jugular, 

 and the sciatic are the paired, the retroperitoneal sac and the 

 ci sterna chyli are the unpaired. It is the retroperitoneal sac which 

 especially concerns us in this paper, for it is the source of the lym- 

 phatics of the intestine. This primitive system is complete and can 

 be injected in pig embryos 2.7 cm. long. 



The idea that the sacs form a primitive lymphatic system is 

 not the most fundamental conception of this new theory, but rather 

 that these sacs arise from the veins and in turn give rise to the lym- 

 phatic vessels, so that we may say that the lymphatic system as 

 a whole is derived from the blood vascular system, that lymphatics 

 are modified veins, and that the growth of lymphatics is always 

 from center to periphery. There is now a general agreement in 

 regard to the origin of the primitive sacs, but in regard to the second 



The American Journal of Anatomy. — Vol. IX, No. 1. 



