Embryonic history of the aortic arches in mammals. 



389 



that the left fourth arch becomes the arch of the aorta, and there is but 

 one ductus Botalli. The reptiles, amj)hibia and fishes are then compared, 

 in so far as the limited knowledge of the aortic arches in these verte- 

 brates would permit. This paper is not illustrated, but it contains the 

 foundations of our knowledge with reference to the development and 

 transformations of the aortic arches. 



The current diagrams, showing the development and transformation 

 of aortic arches, are related in such a way to the older ones, that it has 

 seemed best to notice the earlier papers dealing with the subject. Other- 

 wise, some of these historical references might have been passed over. 



HUSCHKE in 1827 — 28 published an illustrated article on the branchial 

 region of the chick, showing by diagrams three pairs of aortic arches, 

 those now recognized as the third, fourth, and sixth pairs. His observations 

 begin with the fourth day of development, and he therefore missed the 

 history of the first two pairs of arches. Text-Fig. B, taken from: Isis 



Fig. B. 



Aortic arches of an embryo chick at the end of the fourth day, after Huschke, 



in: Isis, 1828. 1 heart, 2, 3, 4 aortic arches, 6 arteria anonyma, 9 pulmonary 



artery, 10 future ductus arteriosus. 



for 1828, shows that Huschke figured with accuracy the three posterior 

 arches in a chick of four days. In describing their transformation how- 

 ever, he ascribed the pulmonary to the combination of the left fourth, 

 and the right fifth arch, as VON Baee had done. He also believed the 

 ductus Botalli to be formed from a portion of the right aortic root as is 

 shown at 10 in Text-Fig. B. HusCHKE shows no subclavians ; the deriva- 

 tives of the third pair of arches not being understood at this time. 



Von Baer in his monumental work „Über Entwickelungsgeschichte 

 der Tiere", 1828, described and figured diagrammatically five pairs of 

 aortic arches in the chick embryo, and showed their fate. His results 

 were published in the previous year in Buedach's Physiology from which 



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