THE DEVELOPMENT OF THE AORTA AND AORTIC 

 ARCHES IN RABBITS 



JOHN LEWIS BREMER 



From the Harvard Medical School, Boston 



NINE FIGURES 



The development of the primary blood-vessels in the body of 

 the embryo has for many years been a matter of dispute. Evans, 

 in the German edition of the second volume of the Keibel-Mall 

 Embryology, sums up the matter as follows: 1 



Whether the first blood-vessels of the embryonic body arise by in- 

 growth from the yolk-sac capillaries, or whether the embryonic vessel- 

 stems, or at least a part of them, originate in situ from the mesoderm 

 of the body, is still an open question. Both views have found their 

 supporters ; the name of His is connected with the first mentioned idea, 

 the names of Riickert and Mollier especially with the second. 



In birds it is possible to prove that the greater part of the de- 

 scending aortae develop from the mesial border of the capillary 

 plexus which has extended in from the yolk-sac, and this is very 

 probably true of mammals also ; but (to quote again) : 



For the cranial part of the aorta, on the other hand, the results are 

 contradictory. His describes it as arising from a further ingrowth of 

 the same extra-embryonic capillaries which form the aorta in its more 

 caudal portion; the capillary chain grows finally over the blind end of 

 the pharynx, turns ventral-ward, and joins the cranial part of the heart 

 cavity. In rebuttal, Riickert and Mollier have stated in numerous 

 articles that the aortae arise in loco from cells of the visceral layer of 

 the mesoderm. It is impossible at present to insist that the anlagen 

 found on the yolk-sac are the only ones for the endothelium of the body 

 vessels. (Keibel-Mall Entwickelungsgeschichte, vol. 2, p. 552, etc.) 



1 In the American edition of this work some of the results of the present paper 

 have been added. 



Ill 



