28 C. W. M. Poynter 
to explain it as an aberrant vessel which through some need has 
reached the proportions of an aorta is to rob any vascular anomaly 
we do not understand of its embryonal significance and reaffirm 
the theory of Baader. This case is in some respects similar to 
that of Shepherd which is figured in the Hand Book of Medical 
Sciences as fig. 292. In the latter case however we must inter- 
pret the anomalous vessel as representing, in addition to the de- 
scending aorta, one of the segmental vessels and its root. 
Thomson reported a condition which, while not a true arch, 
should be included in the classification as representing an inter- 
mediate condition. In a case of right aortic arch a fibrous cord 
occupied the position of the left descending aorta. A case re- 
ferred to by Curnow (1875) is somewhat similar. 
The case of Jones is very interesting as representing an arrest 
of development at a very early stage for not only do both arches 
persist but there are two dorsal aortae as well. 
The description given by McKee is somewhat confusing, but it 
seems to me that this case should be interpreted as a case of right 
aortic arch, with anomalous blood supply to the lungs resulting 
from obstruction of the pulmonary trunk. 
C. Persistence of the Right Aortic Arch with Partial or Complete 
Obliteration of the Left Fourth Arch 
This condition is commonly spoken of as “right aortic arch” 
from which it might be concluded that the normal process of de- 
velopment is simply reversed on the two sides ; however an exam- 
ination of the cases shows a number of different conditions which 
fall into the following classes. 
1. Persistence of the right arch, right dorsal aorta and left 
arch with obliteration of the left dorsal aorta. 
2. Persistence of right aortic arch, left ventral root and left 
dorsal aorta with obliteration of the fourth dorsal root and arch 
on the left. 
3. Persistence of the right aortic arch, left aortic arch and left 
dorsal aorta with obliteration of the left dorsal root. 
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