ON THE FATE OF THE POSTERIOR CARDINAL VEINS AM) THEIR RELATION 



TO THE DEVELOPMENT OF THE VENA CAYA AND 



A/YliOS IN THE EMBRYO IMC. 



BY FLORENCE K. SABIN. 



INTRODUCTION. 



During a study of the lymphatic system in the pig, it became evident that a much more 

 exact knowledge of the details of the development of the prevertehral veins was essential in 

 order to trace the origin of the thoracic duct. A knowledge of the neighboring veins is more 

 necessary for the study of the thoracic duct than for any of the superficial lymphatic trunks, 

 since the latter can be so much more readily injected. Besides their relation to the lym- 

 phatic problem, the azygos veins have proven to be of great interest on the one hand, in 

 connection with their relation to the fate of the posterior cardinal veins, and on the other, in 

 connection with the larger subject of the origin of the vena ava and the primitive veins of 

 the body- wall. 



In the course of this study it has been found that the posterior cardinal veins, which 

 develop in the border of the Wolffian body, disappear entirely with that organ; and that 

 the azygos veins are new prevertebral veins which develop in connection with the vertebra; 

 and subsequently drain the blood from the spinal and intercostal veins as the posterior 

 cardinal veins disappear. It has been shown that the inferior vena cava is not as complex 

 in its development as has been thought. It develops primarily to drain the Wolffian bodies. 

 It has a ventral segment and a dorsal, post-renal segment. The ventral segment comes from 

 two primitive veins, namely, the omphalo-mesenteric and the mesial cardinal (subcardinal ) 

 veins. The dorsal segment comes from a prevertebral plexus. This prevertebral plexus 

 is extensive and from it the following veins develop: the azygos and hemiazygos systems, 

 the post-renal segment of the inferior vena cava, and the ascending lumbar veins. This 

 study has been made possible through the use of two methods, first, the injection of the 

 vascular system of embryos, and secondly, the clearing of total specimens, which we <>\\c 



to Spalteholz. 



TECHNIQUE. 



The methods of injecting embryos have developed as follows: The first extensive 

 description of the methods of injecting embryonic blood- vessels was given by Popoff in 

 1894, in a study of the blood-vessels of the yolk-sac of the chick. He did not make a study 

 of the blood-vessels within the embryo. Popoff brought out the fact that notwithstanding 

 the many studies on the blood-vessels of the yolk-sac, it had been impossible to make out 

 the richness of the vascular net without injections. The technique which he developed is 

 as follows: In general he used line glass canulse to puncture the vessel. The camihr were 

 made by drawing out soft glass tubing of a diameter of 0.5 mm., taking rare that the tube 

 should narrow rapidly to a point. To this canula was attached a rubber tube ending in a 

 small mouthpiece. The pressure was made by blowing into the tube and the fluid used was 

 an aqueous Prussian blue. The place of injection varied according to the stage of develop- 

 ment and the area desired; the most difficult stages were the early ones before t he marginal 

 sinus was fully developed; from this time up to the fourth day the marginal sinus was 



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