Sis INTRODUCTION 
For a number of years I have been interested in the arterial 
variations which have been encountered in my dissecting rooms. 
Notes have been made of these abnormalities and the literature 
describing similar conditions has been gradually collected. The 
more recent textbooks in anatomy devote little space to the sub- 
ject of arterial variations and the classic works which have re- 
viewed the field are no longer readily consulted; then, too, new 
facts have been added to our knowledge of arterial development 
since the most recent of the latter were published. In view of 
these facts it has seemed worth while to assemble the cases I have 
collected from the various sources and classify them according to 
our present knowledge of development. 
I wish to take this opportunity to express my thanks to Doctor 
W. F. Whitney, curator of the anatomical museum at’ Harvard 
Medical School, for placing the splendid collection of the Warren 
Museum at my disposal for study. In the later pages I have 
used the results of my study freely, referring to the various 
anomalies as from the Warren Museum. 
The following does not purport to be the entire list of all 
cases reported, for it was not possible with the library facilities 
and time I had at my disposal to consult all the works that might 
contain a record of such variations, but I believe a sufficient num- 
ber have been collected on which to base reliable conclusions of 
the scope and possibly relative frequency of such abnormalities. 
The bibliography at the end of this study includes not only 
the cases referred to in the body of the work but, in addition, 
many titles which I was unable to consult but which came to me 
on good authority. I have included the latter believing that a full 
bibliography on any subject has a distinct value of its own. 
In this study I have confined the observations to those anom- 
alies directly related to the aortic arches and the ventral aorta. 
In many cases the factor which has produced these variations 
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