AORTIC ARCHES OF BIRDS — GLENNY 527 



contributions on the carotid arteries in birds was overlooked by most 

 workers. Even Forbes and Beddard failed to interpret Garrod's 

 studies satisfactorily, but Boas, Rathke, and Sabatier were better 

 received by most of their contemporaries, with the result that many 

 of their contributions and writings have been passed on to the present 

 time. With respect to their interpretations of the arrangement in 

 birds of the arteries and, especially, the aortic arches, they were in- 

 correct in certain important details. Although Brenner had ques- 

 tioned Rathke's and Sabatier's placement of the subclavian artery as 

 early as 1883, most textbooks in comparative anatomy still carry 

 plates of the Rathke-Boas type of schematic diagrams. 



In spite of correct information presented by Gadow, Hertwig, 

 Hochstetter, and others, only a few textbook writers have made an 

 effort to present the facts in preference to the presentation of a plan 

 of organization or a pattern of evolution in the aortic arch system of 

 the vertebrates. 



A great deal of research was necessary even after the end of the 19th 

 century in order to clarify the true nature of the aortic arch system 

 and the changes wliich these and associated vessels undergo during 

 embryonic development. The greatest single contribution of this 

 kind was made at Northwestern University under the direction of 

 W. A. Locy. Significant contributions on the embryonic develop- 

 ment of arteries in birds were made during the first 6 years of the 20th 

 century by Rabl, Sabin, Locy, and Twining. Thereafter, little work 

 of importance reached the literature until 1934 when Hughes published 

 his very important studies on the development of the cephalic blood 

 vessels in the chick. 



Despite these studies, a great gap still exists insofar as the develop- 

 ment of the coracoid or sternoclavicular, thoracic or intercostal 

 (internal mammary), and pectoral arteries of birds are concerned, 

 I have been unable to find a single reliable account of the exact 

 development of these vessels. Most anatomical references allude to 

 the mammalian condition insofar as it is known, but actual accounts 

 for birds appear to be lacking. 



Apparently, there was little interest in the arterial system of adult 

 birds (for well over a quarter of a century) until I began systematic 

 studies of the arteries of the neck and thorax. Shortly thereafter 

 Bhadiu-i and Biswas began a similar series of studies in India, and a 

 few other incidental papers have appeared from time to time, treat- 

 ing largely with anomalous occurrence of vestiges of embryonic 

 vessels. 



As a result of these studies, I feel that it is weU to summarize the 

 findings of earlier and present-day workers in such a way that future 

 workers may be better able to interpret their findings. It is with 

 this in mind that I propose to discuss the significant changes in the 



